Method for promoting anaerobic fermentation of kitchen garbage by graphene aerogel

Abstract

The invention provides a method for promoting anaerobic fermentation of kitchen garbage through graphene aerogel, and belongs to the technical field of anaerobic methanation. According to the method, the graphene aerogel is added into a kitchen waste anaerobic fermentation system, and constant-temperature anaerobic fermentation is carried out. Compared with the prior art, the preparation method disclosed by the invention has the advantages that the methane yield and the anaerobic fermentation performance are effectively improved by utilizing good electrical properties and surface biocompatibility of the graphene aerogel, and the problem of toxicity of a free graphene nano material is also overcome.

Description

Technical Field

[0001] The present invention relates to the technical field of anaerobic methanogenesis, and in particular to a method for promoting anaerobic fermentation of kitchen waste by using graphene aerogel. Background Art

[0002] Anaerobic fermentation of kitchen waste can not only effectively treat the waste, but also produce biogas, which can be converted into renewable energy such as methane, thus achieving the harmlessness, reduction and resource utilization of kitchen waste. However, at present, the biogas produced by anaerobic fermentation of kitchen waste has a high carbon dioxide content and a low methane content, and the resource utilization efficiency is not high. Therefore, it is necessary to strengthen the methane production effect of anaerobic fermentation and reduce the carbon dioxide production.

[0003] Previous studies have found that adding conductive carbon material graphene to the anaerobic fermentation system can increase the cumulative methane production and promote the degradation of organic matter. However, the π-π interaction and van der Waals force between graphene sheets will cause them to stack and agglomerate, thereby reducing the specific surface area and seriously affecting the electrical properties. Aerogel is a gas-solid two-phase porous material composed of a three-dimensional nano-solid skeleton and a gas filled in the gaps. It has excellent properties such as high porosity (90-99%), high specific surface area, and low density. Graphene aerogel is a three-dimensional network structure carbon material that has the characteristics of light weight, high porosity, and high specific surface area of ​​aerogel. It also has good electrical properties and surface biocompatibility. It can not only avoid the problem of easy stacking and agglomeration between graphene sheets, but also overcome the toxicity of free graphene nanomaterials. Therefore, graphene aerogel can be added as an additive to the anaerobic fermentation system of kitchen waste to increase methane production and anaerobic fermentation performance. Summary of the invention

[0004] The purpose of the present invention is to provide a method for promoting anaerobic fermentation of kitchen waste by using graphene aerogel, so as to overcome the problems of easy accumulation and agglomeration between graphene sheets and toxicity of free graphene nanomaterials, thereby solving the problems of high carbon dioxide content, low methane content and low resource utilization efficiency in biogas produced by anaerobic fermentation of kitchen waste.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The invention provides a method for promoting anaerobic fermentation of kitchen waste by using graphene aerogel. Kitchen waste, inoculated sludge and graphene aerogel are mixed and fermented at a constant temperature in an anaerobic environment.

[0007] Furthermore, the ratio of the kitchen waste to the inoculated sludge is 1:1-2, calculated based on the volatile solid content of the raw materials;

[0008] The added amount of the graphene aerogel is 5 to 100 mg / L.

[0009] Furthermore, the kitchen waste is subjected to centrifugal treatment, and the inoculated sludge is anaerobic granular sludge in an anaerobic reactor for sewage treatment.

[0010] Furthermore, the centrifugal speed is 4000-10000 r / min, and the centrifugal time is 3-10 min.

[0011] Furthermore, the method for preparing the graphene aerogel comprises the following steps:

[0012] Step 1): mixing graphene oxide powder in water for dispersion to obtain a graphene oxide dispersion;

[0013] Step 2): The graphene oxide dispersion and L-ascorbic acid are mixed, and then reduction, freeze-thaw, secondary reduction and freeze-drying are performed in sequence to obtain graphene aerogel.

[0014] Furthermore, in step 1), the dispersion frequency is 30 to 50 Hz, and the dispersion time is 20 to 40 min;

[0015] The concentration of the graphene oxide dispersion is 2-6 g / L.

[0016] Furthermore, in step 2), the usage ratio of the graphene oxide dispersion and L-ascorbic acid is 8-10 mL: 70-100 mg.

[0017] Furthermore, in step 2), the reduction temperature is 75-90° C., and the reduction time is 50-70 min;

[0018] The freezing temperature of the freeze-thaw process is -15 to -20°C, the freeze-thaw time is 1.5 to 3 hours, and the number of freeze-thaw cycles is 2 to 5 times.

[0019] Furthermore, in step 2), the temperature of the secondary reduction is 75 to 90° C., and the time of the secondary reduction is 5 to 7 hours; the temperature of the freeze-drying is -60 to -30° C., and the time of the freeze-drying is 20 to 30 hours.

[0020] Furthermore, the temperature of the constant temperature fermentation is 35-40°C, and the rotation speed of the constant temperature fermentation device is 100-150r / min.

[0021] Beneficial effects of the present invention:

[0022] (1) Graphene aerogel can not only avoid the problem of easy stacking and agglomeration between graphene sheets, but also overcome the toxicity problem of free graphene nanomaterials.

[0023] (2) Graphene aerogel has the characteristics of good conductivity, high porosity, and high specific surface area, which can not only induce and enhance interspecies electron transfer between methanogens, but also provide abundant adsorption sites and enrichment cavities for microorganisms, creating a more favorable microecological environment, thereby enriching methanogens and increasing methane production. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a comparison chart of the cumulative methane production from anaerobic fermentation of kitchen waste after adding graphene aerogel to Comparative Example 1 and Examples 1 to 3, wherein CK is Comparative Example 1; GA5 is Example 1; GA25 is Example 2; and GA50 is Example 3. DETAILED DESCRIPTION

[0025] The invention provides a method for promoting anaerobic fermentation of kitchen waste by using graphene aerogel. Kitchen waste, inoculated sludge and graphene aerogel are mixed and fermented at a constant temperature in an anaerobic environment.

[0026] In the present invention, the ratio of the kitchen waste to the inoculated sludge is 1:1-2, preferably 1:1.2, calculated based on the volatile solid content of the raw materials;

[0027] The addition amount of the graphene aerogel is 5 to 100 mg / L, preferably 10 to 80 mg / L, more preferably 40 to 75 mg / L, and more preferably 50 mg / L.

[0028] In the present invention, the added amount of the graphene aerogel is calculated according to the effective working volume of the anaerobic fermentation environment.

[0029] In the present invention, the kitchen waste is centrifuged, and the inoculated sludge is the anaerobic granular sludge in the sewage treatment anaerobic reactor.

[0030] In the present invention, the kitchen waste is crushed and then centrifuged, and the kitchen waste is deoiled and dehydrated by centrifugation.

[0031] In the present invention, the centrifugal speed is 4000-10000 r / min, preferably 5000-9000 r / min, more preferably 6000 r / min, and the centrifugal time is 3-10 min, preferably 5-8 min, more preferably 7 min.

[0032] In the present invention, the method for preparing the graphene aerogel comprises the following steps:

[0033] Step 1): mixing graphene oxide powder in water for dispersion to obtain a graphene oxide dispersion;

[0034] Step 2): The graphene oxide dispersion and L-ascorbic acid are mixed, and then reduction, freeze-thaw, secondary reduction and freeze-drying are performed in sequence to obtain graphene aerogel.

[0035] In the present invention, the graphene powder preferably has a purity of >99.9%, a single-layer flake diameter of 0.2-10 μm, and a particle size of <80 mesh.

[0036] In the present invention, in step 1), a homogeneous graphene oxide dispersion is obtained after the dispersion, and is preferably stored at a low temperature for future use.

[0037] In the present invention, in step 1), the dispersion is preferably ultrasonic dispersion, the dispersion frequency is 30 to 50 Hz, preferably 35 to 45 Hz, more preferably 40 Hz, and the dispersion time is 20 to 40 min, preferably 30 min;

[0038] The concentration of the graphene oxide dispersion is 2 to 6 g / L, preferably 3 to 5 g / L, and more preferably 4 g / L.

[0039] In the present invention, in step 2), the usage ratio of the graphene oxide dispersion and L-ascorbic acid is 8-10 mL:70-100 mg, preferably 9 mL:80-90 mg, and more preferably 9 mL:85 mg.

[0040] In the present invention, the mixing of the graphene oxide dispersion and L-ascorbic acid is carried out in a vortex oscillator, and the oscillation speed is preferably 2000 r / min and the time is preferably 5 min.

[0041] In the present invention, in step 2), the reduction temperature is 75-90°C, preferably 80-85°C, more preferably 83°C, and the reduction time is 50-70min, preferably 55-65min, more preferably 60min;

[0042] The freezing temperature of the freeze-thaw process is -15 to -20°C, preferably -18°C, the freeze-thaw time is 1.5 to 3 hours, preferably 2 to 2.5 hours, more preferably 2.3 hours, and the number of freeze-thaw cycles is 2 to 5 times, preferably 3 times.

[0043] In the present invention, in step 2), the reduction is followed by natural cooling and then freeze-thawing.

[0044] In the present invention, in step 2), the temperature of the secondary reduction is 75 to 90°C, preferably 78 to 85°C, and more preferably 80°C, and the time of the secondary reduction is 5 to 7h, and more preferably 6h; the temperature of the freeze-drying is -60 to -30°C, preferably -50 to -40°C, and more preferably -45°C, and the time of the freeze-drying is 20 to 30h, preferably 23 to 28h, and more preferably 25h.

[0045] In the present invention, the temperature of the constant temperature fermentation is 35-40°C, preferably 37°C, and the constant temperature fermentation is carried out in a reactor. The rotation speed of the reactor is 100-150r / min, preferably 110-140r / min, and more preferably 130r / min.

[0046] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0047] Example 1

[0048] 0.4 g of graphene oxide was mixed with 100 mL of deionized water, and an ultrasonic machine was used to perform ultrasonic treatment at 40 Hz for 30 min to obtain a homogeneous graphene oxide dispersion, which was stored at low temperature for later use; 10 mL of the graphene oxide dispersion was mixed with 80 mg of L-ascorbic acid, and oscillated at 2000 r / min for 5 min, and then placed in an 80°C oven for reduction for 60 min, then taken out and cooled naturally, and transferred to -18°C for repeated freeze-thaw for 3 times, each time for 2 h; after the freeze-thaw was completed, it was transferred to 80°C for secondary reduction for 6 h, and then freeze-dried at -50°C for 24 h to obtain a graphene aerogel;

[0049] After the kitchen waste is crushed, it is centrifuged at a speed of 6000r / min for 10min to remove oil and water;

[0050] 46g of kitchen waste and 153g of inoculated sludge were added to a 500mL anaerobic fermentation reaction bottle, with an effective working volume of 200mL. 5mg / L of graphene aerogel was added, stirred evenly, filled with nitrogen, and sealed in a constant temperature reactor at a speed of 120r / min and a temperature of 37°C for anaerobic fermentation for 24h. The gas production was recorded using the drainage method, and the methane production was 121.40±0.82mL / g VS.

[0051] Example 2

[0052] Different from Example 1, in this example, the addition amount of graphene oxide aerogel is 25 mg / L, and the methane production is 161.38±1.08 mL / gVS.

[0053] Example 3

[0054] Different from Example 1, in this example, the addition amount of graphene oxide aerogel is 50 mg / L, and the methane yield is 127.52±1.08 mL / gVS.

[0055] Example 4

[0056] 0.2 g of graphene oxide was mixed with 100 mL of deionized water, and an ultrasonic machine was used to perform ultrasonic treatment at 30 Hz for 20 min to obtain a homogeneous graphene oxide dispersion, which was stored at low temperature for later use; 10 mL of the graphene oxide dispersion was mixed with 70 mg of L-ascorbic acid, and oscillated at 2000 r / min for 5 min, and then placed in a 75°C oven for reduction for 70 min, then taken out and cooled naturally, and transferred to -20°C for repeated freeze-thaw twice, each time for 1.5 h; after the freeze-thaw was completed, it was transferred to 75°C for secondary reduction for 5 h, and then freeze-dried at -60°C for 20 h to obtain graphene aerogel;

[0057] After the kitchen waste is crushed, it is centrifuged at a speed of 4000r / min for 10min to remove oil and water;

[0058] Into an anaerobic fermentation reaction bottle with a volume of 500 mL, 46 g of kitchen waste and 153 g of inoculated sludge were added, and the effective working volume was 200 mL. 100 mg / L of graphene aerogel was added, stirred evenly, filled with nitrogen, and sealed, and anaerobic fermentation was carried out in a constant temperature reactor at a speed of 100 r / min and a temperature of 35°C for 24 hours.

[0059] Example 5

[0060] 0.6 g of graphene oxide was mixed with 100 mL of deionized water, and an ultrasonic machine was used to perform ultrasonic treatment at 50 Hz for 20 min to obtain a homogeneous graphene oxide dispersion, which was stored at low temperature for later use; 8 mL of graphene oxide dispersion was mixed with 70 mg of L-ascorbic acid, and oscillated at 2000 r / min for 5 min, and then placed in a 90°C oven for reduction for 50 min, then taken out and cooled naturally, and transferred to -20°C for repeated freeze-thaw for 5 times, each time for 1.5 h; after the freeze-thaw was completed, it was transferred to 90°C for secondary reduction for 5 h, and then freeze-dried at -30°C for 30 h to obtain graphene aerogel;

[0061] After the kitchen waste is crushed, it is centrifuged at a speed of 10,000 r / min for 3 min to remove oil and water;

[0062] Into an anaerobic fermentation reaction bottle with a volume of 500 mL, 46 g of kitchen waste and 153 g of inoculated sludge were added, and the effective working volume was 200 mL. 100 mg / L of graphene aerogel was added, stirred evenly, filled with nitrogen, and sealed, and anaerobic fermentation was carried out in a constant temperature reactor at a speed of 100 r / min and a temperature of 40°C for 24 hours.

[0063] Comparative Example 1

[0064] Different from Example 1, in this comparative example, the amount of graphene oxide added was 0, and the methane yield was 97.90±0.93 mL / g VS.

[0065] Table 1 shows the methane production of Examples 1 to 3 and Comparative Example 1.

[0066] Table 1 Methane production of Examples 1 to 3 and Comparative Example 1

[0067]

[0068] As can be seen from Table 1, the methane production of Examples 1 to 3 is significantly improved compared with that of Comparative Example 1. The graphite aerogel with an addition amount of 25 mg / L has the highest promotion effect, and the methane production is increased by 64.84% compared with Comparative Example 1. 5 mg / L graphene aerogel and 50 mg / L aerogel increase the methane production in anaerobic fermentation by 24.01% and 30.26%, respectively.

[0069] It can be seen from the above embodiments that the present invention provides a method for promoting anaerobic fermentation of kitchen waste by using graphene aerogel. Figure 1 The figure is a comparison of the cumulative methane production of anaerobic fermentation of kitchen waste after adding graphene aerogel in comparative example 1 and examples 1 to 3, wherein CK is comparative example 1, GA5 is example 1, GA25 is example 2, and GA50 is example 3. It can be seen from the figure that adding graphene aerogel to the anaerobic fermentation system of kitchen waste can promote methane production, and when the addition amount is 25 mg / L, the promotion effect is the best. Therefore, the present invention solves the problem that the biogas produced by anaerobic fermentation of kitchen waste in the prior art has a high carbon dioxide content, a low methane content, and a low resource utilization efficiency.

[0070] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for promoting anaerobic fermentation of kitchen waste using graphene aerogel, characterized in that: Kitchen waste, inoculated sludge and graphene aerogel are mixed and fermented at a constant temperature in an anaerobic environment.

2. The method of using graphene aerogel to promote anaerobic fermentation of kitchen waste according to claim 1, characterized in that: Calculated based on the volatile solid content of the raw materials, the ratio of the kitchen waste to the inoculated sludge is 1:1-2; The added amount of the graphene aerogel is 5 to 100 mg / L.

3. The method for promoting anaerobic fermentation of kitchen waste by using graphene aerogel according to claim 1, characterized in that: The kitchen waste is centrifuged, and the inoculated sludge is the anaerobic granular sludge in the sewage treatment anaerobic reactor.

4. The method for promoting anaerobic fermentation of kitchen waste by using graphene aerogel according to claim 3, characterized in that: The centrifugal speed is 4000-10000 r / min, and the centrifugal time is 3-10 min.

5. The method for promoting anaerobic fermentation of kitchen waste by using graphene aerogel according to claim 1, characterized in that: The method for preparing the graphene aerogel comprises the following steps: Step 1): mixing graphene oxide powder in water for dispersion to obtain a graphene oxide dispersion; Step 2): The graphene oxide dispersion and L-ascorbic acid are mixed, and then reduction, freeze-thaw, secondary reduction and freeze-drying are performed in sequence to obtain graphene aerogel.

6. The method for promoting anaerobic fermentation of kitchen waste by using graphene aerogel according to claim 5, characterized in that: In step 1), the dispersion frequency is 30 to 50 Hz, and the dispersion time is 20 to 40 minutes; The concentration of the graphene oxide dispersion is 2-6 g / L.

7. A method for promoting anaerobic fermentation of kitchen waste by using graphene aerogel according to claim 5 or 6, characterized in that: In step 2), the usage ratio of the graphene oxide dispersion and L-ascorbic acid is 8-10 mL:70-100 mg.

8. The method for promoting anaerobic fermentation of kitchen waste by using graphene aerogel according to claim 7, characterized in that: In step 2), the reduction temperature is 75-90° C. and the reduction time is 50-70 min; The freezing temperature of the freeze-thaw process is -15 to -20°C, the freeze-thaw time is 1.5 to 3 hours, and the number of freeze-thaw cycles is 2 to 5 times.

9. A method for promoting anaerobic fermentation of kitchen waste by using graphene aerogel according to claim 5, 6 or 8, characterized in that: In step 2), the temperature of the secondary reduction is 75 to 90° C., and the time of the secondary reduction is 5 to 7 hours; the temperature of the freeze-drying is -60 to -30° C., and the time of the freeze-drying is 20 to 30 hours.

10. The method for promoting anaerobic fermentation of kitchen waste by using graphene aerogel according to claim 1, characterized in that: The temperature of the constant temperature fermentation is 35-40°C, and the rotation speed of the constant temperature fermentation device is 100-150r / min.

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