Three-stage linkage hydrogen production method based on kitchen waste

Abstract

The invention discloses a three-stage linkage hydrogen production method based on kitchen waste, and relates to the technical field of biological enzymes, and the method comprises the following steps: step I, pretreatment; step II, dark fermentation: the materials treated in the step I are fed into a dark fermentation tank, and clostridium beijerinckii with the preservation number of ATCC (American Type Culture Collection) NO.35702 is inoculated into the dark fermentation tank; step III, light fermentation: feeding the first fermentation liquor into a light fermentation tank, inoculating rhodopseudomonas palustris with the preservation number of CGMCC (China General Microbiological Culture Collection Center) 1.2180, adding MoFe nano particles with the concentration of 50 mg / L-100 mg / L, and collecting gas generated by fermentation. Through three-stage linkage of collaborative pretreatment, dark fermentation and light fermentation, efficient and stable conversion from kitchen waste to hydrogen is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of biological enzymes, in particular to a three-stage linkage hydrogen production method based on kitchen waste. BACKGROUND

[0002] Biohydrogen technology is attracting attention in global energy transformation due to its zero carbon emission characteristics. Using organic waste such as kitchen waste to produce hydrogen through dark fermentation can not only realize waste resourceization, but also produce clean energy, and is considered as one of the most potential technical paths. However, there are many problems in the existing kitchen waste hydrogen production technology. On the one hand, the cellulose and other stubborn structures in kitchen waste lead to low hydrolysis efficiency, so that the utilization rate of microorganisms to the substrate is not high. On the other hand, the end metabolic products of dark fermentation contain a large amount of low molecular organic acids, such as acetic acid and butyric acid. These volatile organic acids will have feedback inhibition effect on hydrogen-producing bacteria, limiting the hydrogen production rate and hydrogen production amount of dark fermentation. SUMMARY

[0003] Therefore, the present application provides a three-stage linkage hydrogen production method based on kitchen waste, which improves the hydrogen production efficiency and hydrogen production amount of kitchen waste by synergistic pretreatment, strain selection and precise fermentation conditions.

[0004] A three-stage linkage hydrogen production method based on kitchen waste, comprising the following steps: Step I, pretreatment: the kitchen waste is placed in an environment of 1.1 MPa to 1.3 MPa and 160°C to 180°C for 10 minutes to 20 minutes to obtain pretreated material, and the particle size of the pretreated material is adjusted to 0.5 mm to 2 mm by grinding or sieving.

[0005] Illustratively, the pretreatment pressure is 1.1 MPa, 1.15 MPa, 1.2 MPa, 1.25 MPa, 1.3 MPa or any value between any two of the above values. Illustratively, the pretreatment temperature is 160°C, 165°C, 170°C, 175°C, 180°C or any value between any two of the above values. Illustratively, the pretreatment time is 10 minutes, 12 minutes, 13 minutes, 15 minutes, 18 minutes, 20 minutes or any value between any two of the above values. Illustratively, the particle size of the pretreated material is adjusted to 0.5 mm, 0.6 mm, 0.8 mm, 1.0 mm, 1.5 mm, 1.8 mm, 2 mm or any value between any two of the above values.

[0006] The present application is used for directional modification of kitchen waste by synergistically adjusting the high-temperature and high-pressure treatment environment and selecting suitable particle size, and further regulating the total carbon content (dry weight) of the kitchen waste ≥40%, the fat content (dry weight) ≤25% and the total nitrogen content ≤6% (dry weight), i.e. the mass ratio of degradable carbohydrates in the pretreated substrate ≥50%, and mainly small molecule sugars (glucose, fructose) and emulsified oil and fat, so as to match the carbon source preference of Clostridium beijerinckii (especially ATCC NO.35702) and lay a material foundation for efficient hydrogen production by dark fermentation.

[0007] Step II, dark fermentation: the material pretreated in step I is sent into a dark fermentation tank, and Clostridium beijerinckii with preservation number ATCC NO.35702 is inoculated at an inoculation amount of 10%-15% of the volume of the material, the temperature in the tank is controlled at 33-37℃, the pH value in the tank is controlled at 5.0-6.0, and the material is retained for 2-3 days to obtain a first fermentation liquid.

[0008] Exemplarily, the inoculation amount is 10%, 11%, 12%, 13%, 14%, 15% of the volume of the material or any value between any two of the above values. Exemplarily, the pH value in the tank is 5.0, 5.2, 5.3, 5.5, 5.6, 5.8, 5.9, 6.0 or any value between any two of the above values.

[0009] In the first fermentation liquid produced by dark fermentation, butyric acid accounts for 60%-70% of the total volatile fatty acid (VFA) (only 30%-40% in the traditional process), and butyric acid is the optimal substrate for Rhodopseudomonas palustris. Through the above pretreatment process and the selection of dark fermentation strains and environment, the molar ratio of butyric acid to acetic acid in the first fermentation liquid is ≥1.5, which creates ideal conditions for secondary hydrogen production by light fermentation.

[0010] Step III, light fermentation: the first fermentation liquid is sent into a light fermentation tank, and Rhodopseudomonas palustris with preservation number CGMCC 1.2180 is inoculated at an inoculation amount of 20%-25% of the volume of the first fermentation liquid, the light fermentation tank is made of transparent material, and a LED array with a wavelength of 590±10nm is built in, the light intensity is 5000-10000 lux, the temperature is 30±1℃, 50-100 mg / L of MoFe nanoparticles are added, and the gas produced by fermentation is collected.

[0011] Exemplarily, the inoculation amount is 20%, 21%, 22%, 23%, 24%, 25% or any value between any two of the above of the volume of the first fermentation liquid. Exemplarily, the addition amount of MoFe nanoparticles is 50 mg / L, 60 mg / L, 70 mg / L, 80 mg / L, 90 mg / L, 100 mg / L or any value between any two of the above.

[0012] The Rhodopseudomonas palustris with the preservation number CGMCC 1.2180 is selected in the present application, and the light absorption efficiency of the photosynthetic pigment thereof to red light at a wavelength of 590±10 nm is the highest (increased by 30% compared to white light irradiation). Meanwhile, an LED array at the wavelength is built in to activate photosystem II to provide sufficient energy for hydrogen production, and the organic acids (butyric acid, acetic acid) produced by dark fermentation are further converted into hydrogen, so that the total hydrogen production is increased by 75% compared to single dark fermentation. It can be seen that the Rhodopseudomonas palustris with the preservation number CGMCC 1.2180 can better decompose the first fermentation liquid obtained by pretreatment and dark fermentation, and further improve the hydrogen production efficiency and hydrogen production.

[0013] In some embodiments, the kitchen waste satisfies: total carbon content (on a dry weight basis) ≥ 40%, the proportion of degradable carbohydrates in the total carbon content of the kitchen waste ≥ 50%, fat content (on a dry weight basis) ≤ 25% and total nitrogen content ≤ 6% (on a dry weight basis), salt content (calculated as NaCl) ≤ 3%, and total heavy metal content ≤ 10 mg / kg. In this way, it is more conducive to matching Clostridium beijerinckii with the ATCC NO. 35702 number.

[0014] In some embodiments, in step I, the pretreatment further includes: adding 0.5%-1% of a surfactant, and the surfactant includes polysorbate 80.

[0015] Exemplarily, the addition amount of the surfactant is 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1% or any value between any two of the above.

[0016] An appropriate amount of polysorbate 80 can emulsify the oil in the kitchen waste (especially for substrates with a fat content ≤ 25%), further reduce the solid-liquid interfacial tension, increase the substrate dispersibility by more than 40%, enhance the contact efficiency of the hydrogen-producing bacteria and the carbon source, and further increase the dark fermentation hydrogen production rate.

[0017] Especially, when the fat content is 15%-25%, the addition amount of polysorbate 80 is 0.8%-1%; and when the fat content is ≤ 15%, the addition amount is 0.5%-0.7%.

[0018] In some embodiments, in step III, the photobioreactor is connected to a hydrogen-permeable membrane separation system, the hydrogen-permeable membrane comprises a palladium-silver alloy membrane supported by porous ceramic, the mass percentage of palladium in the alloy is 75% to 80%, and the residence time of the gas produced by the photobioreaction in the hydrogen-permeable membrane separation system is 20 minutes to 30 minutes.

[0019] For example, the mass percentage of palladium in the alloy is 75%, 76%, 77%, 78%, 79%, 80%, or any value between any two of the above values.

[0020] For example, the residence time of the gas produced by the photobioreaction in the hydrogen-permeable membrane separation system is 20 minutes, 22 minutes, 24 minutes, 25 minutes, 26 minutes, 28 minutes, 30 minutes, or any value between any two of the above values.

[0021] In some embodiments, in step II, the headspace oxygen content of the dark fermentation tank is controlled to be ≤0.1% by nitrogen replacement. Precise oxygen control by nitrogen replacement creates a special metabolic environment for hydrogen-producing bacteria, ensuring high dark fermentation yield.

[0022] In some embodiments, in step III, the C / N value of the first fermentation broth is adjusted to (15-20):1 by adding ammonium chloride. Adjusting the C / N value by adding ammonium chloride allows the carbon source to be preferentially used for hydrogen production rather than bacterial growth, thereby achieving efficient conversion of carbon sources during the photobiological fermentation stage and further increasing the total hydrogen production.

[0023] Therefore, the three-stage process of pretreatment, dark fermentation with suitable strains and environment, and further photobiological fermentation with suitable strains and environment is the core of the present application. First, the mass percentage of degradable carbohydrates in the kitchen waste is regulated to be ≥50%, with small molecule sugars (glucose, fructose) and emulsified oil and fat being the main components. Then, the kitchen waste is directionally modified by pretreatment to adapt to the carbon source preference of ATCC NO. 35702, and the environment of the dark fermentation is regulated to be suitable, so that the molar ratio of butyric acid to acetic acid in the first fermentation broth is ≥1.5. Then, an appropriate amount of Rhodopseudomonas palustris with preservation number CGMCC 1.2180 is selected as the inoculation bacteria for photobiological fermentation to adapt to the first fermentation broth as the substrate, which can further convert the organic acids produced by dark fermentation into hydrogen. This synergistic combination achieves directional conversion of the substrate to hydrogen, thereby improving the hydrogen production efficiency and hydrogen production of kitchen waste. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 Figure 1 is a schematic diagram of the three-stage process of the hydrogen production method based on kitchen waste in some embodiments of the present application. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical scheme and advantages of the present application clearer, the present application will be further described in detail below in combination with examples and comparative examples. It should be understood that the specific examples described herein are only used to explain the present application and not to limit the present application.

[0026] A three-stage linkage hydrogen production method based on kitchen waste The kitchen waste satisfies at least one of the following conditions: Condition A, the total carbon content (on a dry weight basis) thereof is ≥40%, wherein the mass of degradable carbohydrates accounts for ≥50% of the total carbon content of the kitchen waste; Condition B, the fat content (on a dry weight basis) thereof is ≤25% and the total nitrogen content is ≤6% (on a dry weight basis); Condition C, the salt content (in terms of NaCl) thereof is ≤3% and the total heavy metal content is ≤10 mg / kg.

[0027] The three-stage linkage hydrogen production method comprises the following steps: Step I, pretreatment The above kitchen waste is placed in an environment of 1.1 MPa-1.3 MPa, 160°C-180°C for 10-20 minutes. In this way, the cellulose-lignin structure of the kitchen waste can be destroyed, the dissolution of carbohydrates is promoted, and the substrate conversion rate is increased by 20%-30%, providing sufficient available carbon source for dark fermentation.

[0028] In step I, the pretreatment further comprises: adding 0.5%-1% of a surfactant, wherein the surfactant comprises polysorbate 80. That is, 0.5%-1% of a surfactant is added to the above kitchen waste, and then placed in an environment of 1.1 MPa-1.3 MPa, 160°C-180°C for 10-20 minutes.

[0029] In this way, the oil in the kitchen waste (especially for substrates with a fat content ≤25%) can be emulsified, the solid-liquid interfacial tension is reduced, the substrate dispersibility is increased by more than 40%, the contact efficiency of hydrogen-producing bacteria and carbon source is enhanced, and the dark fermentation hydrogen production rate is increased.

[0030] After pretreatment, the particle size of the pretreated material is controlled to be 0.5-2 mm by grinding or sieving.

[0031] In this way, the specific surface area of the substrate can be increased by 2-3 times, the contact area of microorganisms is increased, the carbon source dissolution rate is increased by more than 50%, and at the same time, the viscosity of the fermentation broth caused by too fine particle size is avoided (to prevent mass transfer obstruction), ensuring the uniformity of the dark fermentation system and increasing the substrate conversion rate.

[0032] Step II, dark fermentation The pretreated material of step I is sent to a dark fermentation tank, and the headspace oxygen content of the dark fermentation tank is controlled to be less than or equal to 0.1% by nitrogen replacement. Clostridium beijerinckii with the accession number of ATCC NO.35702 is inoculated at an inoculation amount of 10% to 15% of the volume of the material, the tank temperature is controlled to be 33°C to 37°C, and the tank pH value is controlled to be 5.0 to 6.0, and the residence time is 2 to 3 days to obtain a first fermentation liquor.

[0033] The preservation site of Clostridium beijerinckii with the accession number of ATCC NO.35702 is located in Manassas, Virginia, USA, and can be purchased through the authorized dealers of ATCC.

[0034] Clostridium beijerinckii is a strict anaerobe, and precise oxygen control is achieved by nitrogen replacement to create a metabolic environment for hydrogen-producing bacteria, further improving the yield of dark fermentation.

[0035] Step III, photofermentation The first fermentation liquor is sent to a photofermentation tank, and Rhodopseudomonas palustris with the accession number of CGMCC 1.2180 is inoculated at an inoculation amount of 20% to 25% of the volume of the first fermentation liquor. The photofermentation tank is made of transparent material and is internally provided with an LED array with a wavelength of 590±10nm. The light intensity is 5000lux to 10000lux, the temperature is 30±1°C, 50mg / L to 100mg / L MoFe nanoparticles are added, and the gas produced by fermentation is collected.

[0036] The preservation site of Rhodopseudomonas palustris with the accession number of CGMCC 1.2180 is located in the Institute of Microbiology, Chinese Academy of Sciences, and is available for online purchase.

[0037] Optionally, the C / N value of the first fermentation liquor is adjusted to (15 to 20):1 by adding ammonium chloride. The C / N range matches the optimal metabolic demand of Rhodopseudomonas palustris, promotes the synthesis of nitrogen fixation enzymes, and increases the hydrogen production by 25% to 35%. It avoids the synthesis of hydrogen production enzymes being blocked due to insufficient nitrogen, or excessive growth of bacteria due to excessive nitrogen.

[0038] Step IV, separation of hydrogen The photofermentation tank is connected to a hydrogen-permeable membrane separation system, and the residence time of the gas produced by photofermentation in the hydrogen-permeable membrane separation system is 20min to 30min. The hydrogen-permeable membrane includes a palladium-silver alloy membrane supported by porous ceramic, wherein the mass fraction of palladium in the alloy is 75% to 80%. The selective permeation coefficient of the palladium-silver alloy membrane (Pd75% to 80%) supported by porous ceramic for hydrogen is up to 10 -8 ~10 -7 mol·m -1·s -1 ·Pa -1 The hydrogen in the fermentation gas can be separated in real time, avoiding hydrogen dissolution loss, and at the same time, the hydrogen purity is improved to more than 99%.

[0039] The three-level linkage hydrogen production method based on kitchen waste is described below in conjunction with specific examples. Those skilled in the art will understand that the preparation method described in the present application is only an example, and any other suitable preparation method is within the scope of the present application.

[0040] Experimental material preparation Kitchen waste: Collecting cafeteria rice, vegetable leaves, and mixed waste of noodles (dry weight total carbon 42%, degradable carbohydrates accounting for 58% of total carbon, fat 18%, total nitrogen 4.5%, salt content 2.2%, heavy metals 7.3 mg / kg).

[0041] Strain: Clostridium beijerinckii (ATCC NO.35702), activated in reinforced clostridium medium (containing glucose 20 g / L, yeast extract 5 g / L, 35°C anaerobic culture for 48 h).

[0042] Rhodopseudomonas palustris (CGMCC 1.2180), activated in RCVBN medium (containing sodium acetate 1 g / L, 590 nm red light irradiation, 30°C culture for 72 h).

[0043] Reagents: MoFe nanoparticles (average particle size 50 nm, purity 99.9%), polysorbate 80 (analytical pure), ammonium chloride (analytical pure), phosphate buffer (0.1 mol / L, pH 5.5).

[0044] Equipment: High-pressure steam treatment kettle (volume 5 L), colloid mill (rotating speed 3000 r / min), anaerobic fermentation tank (2 L with pH online monitoring), photo-fermentation tank (1 L, borosilicate glass material), 590±10 nm LED array (adjustable light intensity), gas chromatograph (Agilent 7890A, DB-FFAP chromatographic column).

[0045] Detection index and method Hydrogen purity: Gas chromatograph TCD detector (5A molecular sieve column, column temperature 80°C, argon carrier gas); Total hydrogen production: Cumulative drainage volume conversion (standard state); Fermentation broth composition: HPLC (Aminex HPX-87H column, 0.05 mol / L sulfuric acid mobile phase, column temperature 45°C). Example 1

[0046] Step I, pretreatment Steam explosion treatment: 500 g of kitchen waste (wet weight) was put into an autoclave, and the pressure was set to 1.2 MPa and the temperature was set to 170℃. After maintaining for 15 min, the pressure was quickly released, and the treated material was collected. Particle size control: The steam explosion treated material was transferred to a colloid mill, ground for 5 min, and then passed through a 1 mm standard sieve. The undersize material (particle size 0.5 mm ~1 mm) was collected, and the moisture content was measured (controlled at 80±2%).

[0047] Step II, dark fermentation 1 L of pretreated material was added to a 2 L anaerobic fermentation tank, and 120 mL of Clostridium butyricum seed liquid (inoculum 12%) was inoculated. The initial pH was adjusted to 5.5 with phosphate buffer. Environmental parameter control: high-purity nitrogen gas (99.99%) was introduced for 10 min to replace the headspace (oxygen content ≤0.1%), and the temperature was set to 35℃, the stirring speed was set to 120 r / min, and the fermentation was sealed. Process monitoring: 5 mL of sample was taken every 12 h, centrifuged at 12000 r / min for 10 min, and the supernatant was filtered through a 0.22 μm filter membrane. The butyric acid and acetic acid concentrations were detected by gas chromatography (chromatographic conditions: column temperature 120℃, FID detector 200℃, nitrogen carrier gas 1 mL / min). End point determination: after 60 h of fermentation, the butyric acid concentration was measured to be 8.2 g / L, the acetic acid concentration was 4.9 g / L, the molar ratio was 1.67 (≥1.5), and the fermentation was stopped. The first fermentation broth was collected.

[0048] Step III, photo fermentation 500 mL of the first fermentation broth was taken, 125 mL of Rhodopseudomonas palustris seed liquid (inoculum 25%) was inoculated, and 75 mg of MoFe nanoparticles (final concentration 75 mg / L) was added. It was transferred to a photo fermentation tank. Light and temperature control: a 590 nm LED array was turned on, the light intensity was set to 8000 lux, the temperature was maintained at 30℃, and the stirring speed was set to 80 r / min. Gas collection: the produced gas was collected by the drainage method, and the gas production was recorded every 24 h. The continuous fermentation lasted for 96 h.

[0049] Expected results: The hydrogen production in the dark fermentation stage was 120~150 mL / g of volatile solids, and the additional hydrogen production in the photo fermentation stage was 80~100 mL / g of volatile solids. The total hydrogen production rate was increased by 75% compared to single dark fermentation, and the hydrogen purity after membrane separation could reach more than 99.2%. Example 2

[0050] Step I, pretreatment Steam explosion treatment: 500 g of kitchen waste (wet weight) was put into an autoclave, 0.8% polysorbate 80 was added, the pressure was set to 1.2 MPa, the temperature was set to 170°C, and the pressure was maintained for 15 min before rapid pressure relief. The treated material was collected. Particle size control: The steam-treated material was transferred to a colloid mill and ground for 5 min, then passed through a 1 mm standard sieve. The undersize material (particle size 0.5-1 mm) was collected and the moisture content was measured (controlled at 80±2%); Step II, dark fermentation 1 L of pretreated material was added to a 2 L anaerobic fermentation tank, 120 mL of Clostridium butyricum seed liquid was inoculated (inoculum size 12%), and the initial pH was adjusted to 5.5 with phosphate buffer. Environmental parameter control: high-purity nitrogen gas (99.99%) was introduced for 10 min to replace the headspace (oxygen content ≤0.1%), the temperature was set to 35°C, the stirring speed was set to 120 r / min, and the fermentation was sealed. Process monitoring: 5 mL of sample was taken every 12 h, centrifuged at 12000 r / min for 10 min, the supernatant was filtered through a 0.22 μm filter membrane, and the butyric acid and acetic acid concentrations were detected by gas chromatography (chromatographic conditions: column temperature 120°C, FID detector 200°C, nitrogen carrier gas 1 mL / min). End point determination: after 60 h of fermentation, the butyric acid concentration was measured to be 8.2 g / L, the acetic acid concentration was 4.9 g / L, the molar ratio was 1.67 (≥1.5), the fermentation was stopped, and the first fermentation broth was collected.

[0051] Step III, photo fermentation 500 mL of the first fermentation broth was taken, 125 mL of Rhodopseudomonas palustris seed liquid was inoculated (inoculum size 25%), 75 mg of MoFe nanoparticles was added (final concentration 75 mg / L), and it was transferred to a photo fermentation tank. Light and temperature control: a 590 nm LED array was turned on, the light intensity was set to 8000 lux, the temperature was maintained at 30°C, and the stirring speed was set to 80 r / min. Gas collection: the generated gas was collected by the drainage method, and the gas production was recorded every 24 h. The fermentation was continued for 96 h.

[0052] Test results: The hydrogen production in the dark fermentation stage was increased to 135-155 mL / g of volatile solids.

[0053] Compared with Example 1, Example 2 keeps the core parameters of steam explosion (pressure 1.2 MPa, temperature 170℃, holding time 15 min) consistent in the pretreatment stage, and additionally adds 0.6% (mass fraction) of polysorbate 80. Polysorbate 80, as a non-ionic surfactant, can promote the efficiency of steam explosion in destroying the material structure by reducing the solid-liquid interfacial tension of kitchen waste, so that the macromolecular organic matter such as cellulose and hemicellulose in the material is more fully degraded into small molecular soluble carbon sources (such as glucose, fructose, etc.), providing more easily available substrates for subsequent microbial metabolism, and effectively improving the substrate accessibility.

[0054] In the dark fermentation stage, the operating parameters of Example 2 are completely consistent with those of Example 1: take 1L of pretreated material and add 2L of anaerobic fermentation tank, inoculate 120mL of Clostridium beijerinckii (ATCC NO.35702) seed liquid (inoculation amount 12%), adjust the initial pH to 5.5 with phosphate buffer; replace the headspace with 99.99% high-purity nitrogen for 10 min (ensure that the oxygen content in the headspace is ≤0.1%), set the fermentation temperature to 35℃, the stirring speed to 120r / min, and seal the anaerobic fermentation; take 5mL every 12h, centrifuge at 12000r / min for 10min, filter with a 0.22μm filter membrane, and then detect the concentrations of butyric acid and acetic acid by gas chromatography (column temperature 120℃, FID detector temperature 200℃, nitrogen carrier gas flow rate 1mL / min). After 60h of fermentation, Example 3 measured the butyric acid concentration to be 8.2g / L and the acetic acid concentration to be 4.9g / L, with a butyric acid to acetic acid molar ratio of 1.67 (meeting the process requirement of ≥1.5), which is completely consistent with Example 1, indicating that the addition of polysorbate 80 in the pretreatment stage does not have a negative impact on the metabolic pathway and product concentration ratio of Clostridium beijerinckii under the condition of unchanged dark fermentation parameters, ensuring the metabolic stability in the dark fermentation stage.

[0055] The final test results show that the hydrogen production in the dark fermentation stage of Example 2 is increased to 135~155mL / g VS, which is significantly higher than the 120~150mL / g VS of Example 1. Example 3

[0056] Step I, pretreatment Steam explosion treatment: 500g of kitchen waste (wet weight) is put into an autoclave, the pressure is set to 1.2MPa, the temperature is set to 170℃, and after maintaining for 15min, the pressure is quickly released, and the treated material is collected; Particle size control: the material after steam explosion treatment is transferred to a colloid mill, ground for 5min, and then passed through a 1mm standard sieve, and the undersize material (particle size 0.5mm~1mm) is collected, and the moisture content is measured (controlled at 80±2%).

[0057] Step II, dark fermentation Take 1 L of pretreated material into a 2 L anaerobic fermentation tank, inoculate 120 mL of Clostridium butyricum seed liquid (inoculation amount 12%), adjust the initial pH to 5.5 with phosphate buffer; Environmental parameter control: replace the headspace with high-purity nitrogen (99.99%) for 10 min (oxygen content ≤0.1%), set the temperature to 35°C, the stirring speed to 120 r / min, and seal the fermentation tank; Process monitoring: take 5 mL of sample every 12 h, centrifuge at 12000 r / min for 10 min, filter the supernatant through a 0.22 μm filter membrane, and then detect the concentrations of butyric acid and acetic acid by gas chromatography (chromatographic conditions: column temperature 120°C, FID detector 200°C, nitrogen carrier gas 1 mL / min); End point determination: after 60 h of fermentation, the measured butyric acid concentration was 8.2 g / L, the acetic acid concentration was 4.9 g / L, the molar ratio was 1.67 (≥1.5), the fermentation was stopped, and the first fermentation broth was collected.

[0058] Step III, photo fermentation Substrate adjustment: take 500 mL of the first fermentation broth, add ammonium chloride to adjust the C / N to 18:1, measure the pH and adjust it to 7.0; Inoculation and parameter setting: inoculate 125 mL of Rhodopseudomonas palustris seed liquid (inoculation amount 25%), add 75 mg of MoFe nanoparticles (final concentration 75 mg / L), and transfer to a photo fermentation tank; Illumination and temperature control: turn on the 590 nm LED array, set the light intensity to 8000 lux, maintain the temperature at 30°C, and set the stirring speed to 80 r / min; Gas collection: collect the generated gas by the drainage method, record the gas production every 24 h, and continuously ferment for 96 h.

[0059] Test results: The additional hydrogen production in the photo fermentation stage was 90~110 mL / g volatile solid.

[0060] It can be seen that in the photo-fermentation stage, the C / N value of the first fermentation liquor in Example 3 is adjusted to 18:1 by adding ammonium chloride, and the pH value is adjusted to 7.0. The C / N value is a core parameter affecting the growth and hydrogen production activity of the photo-fermentation strain (Rhodopseudomonas palustris, CGMCC1.2180), and a suitable C / N value is beneficial to promoting the growth and reproduction of the strain and hydrogen production metabolism. The subsequent photo-fermentation operation parameters are consistent with those in Example 1: 125 mL of Rhodopseudomonas palustris seed liquor (inoculation amount 25%) is added, 75 mg of MoFe nanoparticles (final concentration 75 mg / L) is added, and then it is transferred to a photo-fermentation tank; a 590 nm LED array is turned on (light intensity 8000 lux), the fermentation temperature is maintained at 30°C, the stirring speed is 80 r / min, the drainage method is used to collect the fermentation gas, and the continuous fermentation is carried out for 96 h.

[0061] Comparative Example 1 Step I, pretreatment Steam explosion treatment: 500 g of kitchen waste (wet weight) is put into an autoclave, the pressure is set to 1.2 MPa, the temperature is set to 130°C, and after maintaining for 15 min, the pressure is quickly released, and the treated material is collected; Particle size control: the steam-treated material is transferred to a colloid mill, ground for 5 min, and then passed through a 1 mm standard sieve, and the undersize material (particle size 0.5-1 mm) is collected, and the moisture content is determined (controlled at 80±2%); Step II, dark fermentation 1 L of pretreated material is added to a 2 L anaerobic fermentation tank, 120 mL of Clostridium butyricum seed liquor (inoculation amount 12%) is added, the initial pH is adjusted to 6.0 with phosphate buffer, the temperature is set to 35°C, the stirring speed is 120 r / min, and the fermentation is carried out in a sealed state; Process monitoring: 5 mL of sample is taken every 12 h, centrifuged at 12000 r / min for 10 min, the supernatant is filtered through a 0.22 μm filter membrane, and the butyric acid and acetic acid concentrations are detected by gas chromatography (chromatographic conditions: column temperature 120°C, FID detector 200°C, nitrogen carrier gas 1 mL / min); End point determination: after 60 h of fermentation, the butyric acid concentration is 7.14 g / L, the acetic acid concentration is 5.1 g / L, the molar ratio is 1.4 (<1.5), the fermentation is stopped, and the first fermentation liquor is collected.

[0062] Step III, photo-fermentation 500 mL of the first fermentation liquor is taken, 125 mL of Rhodopseudomonas palustris seed liquor (inoculation amount 25%) is added, 75 mg of MoFe nanoparticles (final concentration 75 mg / L) is added, and then it is transferred to a photo-fermentation tank; Light and temperature control: a 590 nm LED array is turned on, the light intensity is set to 8000 lux, the temperature is maintained at 30°C, and the stirring speed is 80 r / min; Gas collection: The produced gas was collected by drainage method, and the gas production was recorded every 24 h, and the fermentation was continuously carried out for 96 h.

[0063] Test results: The hydrogen production in the dark fermentation stage was 90-120 mL / g volatile solids, and the additional hydrogen production in the photo fermentation stage was 30-50 mL / g volatile solids.

[0064] In the steam explosion step of the pretreatment in the comparative example 1, the temperature was set to 130°C, which was significantly lower than 170°C in the example 1. Under the same rhythm as the example 1, the butyric acid and acetic acid concentrations were detected every 12 h. After 60 h of fermentation, the butyric acid concentration was 7.14 g / L, the acetic acid concentration was 5.1 g / L, and the molar ratio was 1.4. Compared with the example 1, the butyric acid concentration was slightly lower, the acetic acid concentration was slightly higher, and the molar ratio did not reach the standard of the example 1. In the photo fermentation stage, the operation of the comparative example 1 was basically the same as that of the example 1. 125 mL of Rhodopseudomonas palustris seed solution was introduced, 75 mg of MoFe nanoparticles (final concentration 75 mg / L) was added, the 590 nm LED array was turned on, the light intensity was set to 8000 lux, the temperature was maintained at 30°C, the stirring speed was 80 r / min, the gas was collected by drainage method, and the fermentation was continuously carried out for 96 h. However, due to the difference in the dark fermentation stage, the final hydrogen production was also affected. Compared with the example 1, the hydrogen production in the dark fermentation stage of the comparative example 1 was reduced by about 60 mL / g volatile solids, and the additional hydrogen production in the photo fermentation stage was reduced by about 50 mL / g volatile solids.

[0065] Comparative example 2 Step I, dark fermentation 1 L of material was added to a 2 L anaerobic fermentation tank, 120 mL of Clostridium butyricum seed solution (inoculation amount 12%) was introduced, the initial pH was adjusted to 6.0 with phosphate buffer, the temperature was set to 35°C, the stirring speed was 120 r / min, and the fermentation was sealed. Process monitoring: 5 mL was taken every 12 h, centrifuged at 12000 r / min for 10 min, the supernatant was filtered through a 0.22 μm filter membrane, and the butyric acid and acetic acid concentrations were detected by gas chromatography (chromatographic conditions: column temperature 120°C, FID detector 200°C, nitrogen carrier gas 1 mL / min); After 60 h of fermentation, the butyric acid and acetic acid concentrations were measured, the fermentation was stopped, and the first fermentation liquid was collected.

[0066] Step II, photo fermentation 500 mL of the first fermentation liquid was taken, 125 mL of Rhodopseudomonas palustris seed solution (inoculation amount 25%) was introduced, 75 mg of MoFe nanoparticles (final concentration 75 mg / L) was added, and it was transferred to a photo fermentation tank. Light and temperature control: turn on 590 nm LED array, set light intensity 8000 lux, temperature 30℃, stirring rate 80 r / min; Gas collection: collect the produced gas by drainage method, record the gas production every 24 h, and continuously ferment for 96 h.

[0067] Test results: The molar ratio of butyric acid to acetic acid was 0.76, the hydrogen production in the dark fermentation stage was 80-100 mL / g volatile solids (about 40% lower than that in Example 1), and the additional hydrogen production in the photo fermentation stage was 30-50 mL / g volatile solids.

[0068] Comparative Example 3 Kitchen waste: collect mixed waste of cafeteria rice, vegetable leaves, fatty meat, and fried food (dry weight total carbon 42%, degradable carbohydrates accounting for 46% of total carbon, fat 33%, and total nitrogen 7%).

[0069] The experimental process was completely consistent with that of Example 1.

[0070] Test results: the molar ratio of butyric acid to acetic acid was 0.52, the hydrogen production in the dark fermentation stage was 70-90 mL / g volatile solids (about 40% lower than that in Example 1), and the additional hydrogen production in the photo fermentation stage was 20-35 mL / g volatile solids (about 65% lower than that in Example 1). In Comparative Example 3, the degradable carbohydrates in the kitchen waste were insufficient, which led to insufficient available sugar source in the dark fermentation stage and a decrease in butyric acid production. In addition, the fat content was too high, and high-concentration oil would inhibit the activity of ATCC NO. 35702 and reduce the activity of the bacterial cells in the photo fermentation stage. CGMCC 1.2180 was sensitive to high-oil environments. Therefore, even if suitable pretreatment, dark fermentation, and photo fermentation are used, high-efficiency hydrogen production cannot be achieved by using kitchen waste with inappropriate parameters.

[0071] The above only describes preferred embodiments of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A three-stage linkage method for hydrogen production based on kitchen waste, characterized in that, The kitchen waste satisfies: a total carbon content (on a dry weight basis) of ≥40%, wherein the mass of degradable carbohydrates accounts for ≥50% of the total carbon content of the kitchen waste; and a fat content (on a dry weight basis) of ≤25% and a total nitrogen content of ≤6% (on a dry weight basis); and comprises the following steps: Step I, pretreatment; The kitchen waste is placed in an environment of 1.1 MPa-1.3 MPa, 160°C-180°C for treatment. Step II, dark fermentation; The material pretreated in Step I is sent to a dark fermentation tank, inoculated with Clostridium beijerinckii with accession number ATCC NO.35702, the temperature in the tank is controlled to be 33°C-37°C, the pH value in the tank is controlled to be 5.0-6.0, and the residence time is 2-3 days to obtain a first fermentation liquor. Step III, photo fermentation; The first fermentation liquor is sent to a photo fermentation tank, inoculated with Rhodopseudomonas palustris with accession number CGMCC 1.2180, the photo fermentation tank is made of transparent material, and is internally provided with an LED array with a wavelength of 590±10 nm, the light intensity is 5000 lux-10000 lux, the temperature is 30±1°C, 50 mg / L-100 mg / L MoFe nanoparticles are added, and the gas produced in the fermentation is collected.

2. The three-stage linked hydrogen production method based on kitchen waste according to claim 1, characterized in that, The kitchen waste has a salt content (calculated as NaCl) of ≤3% and a total heavy metal content of ≤10 mg / kg.

3. The three-stage linked hydrogen production method based on kitchen waste according to claim 1 or 2, characterized in that, The kitchen waste is placed in an environment of 1.1 MPa-1.3 MPa, 160°C-180°C for treatment for 10 min-20 min.

4. The three-stage linked hydrogen production method based on kitchen waste according to claim 3, characterized in that, In Step I, the pretreatment further comprises: 0.5%-1% of a surfactant is added, and the surfactant comprises polysorbate 80.

5. The three-stage linked hydrogen production method based on food waste according to claim 1, characterized in that, In Step II, the inoculation amount is 10%-15% of the volume of the material; and / or, In the first fermentation liquor, the molar ratio of butyric acid to acetic acid is ≥1.

5.

6. The three-stage linked hydrogen production method based on food waste according to claim 1, characterized in that, In Step III, the inoculation amount is 20%-25% of the volume of the first fermentation liquor; and / or, The photo fermentation tank is connected to a hydrogen-permeable membrane separation system, the hydrogen-permeable membrane comprises a palladium-silver alloy membrane with a porous ceramic as a support body, and the mass fraction of palladium in the alloy is 75%-80%.

7. The three-stage linked hydrogen production method based on kitchen waste according to claim 6, characterized in that, The residence time of the gas produced in the photo fermentation in the hydrogen-permeable membrane separation system is 20 min-30 min.

8. The three-stage linked hydrogen production method based on food waste according to claim 1, characterized in that, In Step I, after the pretreatment, the following step is further included: The particle size of the pretreated material is adjusted to 0.5 mm-2 mm by grinding or sieving.

9. The three-stage linked hydrogen production method based on kitchen waste according to claim 8, characterized in that, In Step II, the following step is further included: The headspace oxygen content of the dark fermentation tank is controlled to be ≤0.1% by nitrogen replacement.

10. The three-stage linked hydrogen production method based on kitchen waste according to claim 9, characterized in that, In Step III, the following step is further included: The C / N value of the first fermentation liquor is adjusted to (15-20):1 by adding ammonium chloride, and the pH value is controlled to be 6.0-7.0.

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