Method for producing hydrogen by dark fermentation of organic wastewater

Abstract

This invention provides a method for hydrogen production from organic wastewater through dark fermentation, belonging to the field of fermentation hydrogen production technology. The method includes: mixing organic wastewater, biochar loaded with metal nanoparticles, and a domesticated butyric acid-producing mixed bacterial community; performing micro-electrolysis and bioactivation treatment to obtain a pretreated solution; then subjecting the pretreated solution to hydrogen-producing phase fermentation treatment, adding an electron mediator to obtain a fermentation broth containing volatile acids; further, subjecting the fermentation broth to de-inhibition phase treatment, using adsorbent materials to adsorb volatile acids, and simultaneously converting some of the adsorbed volatile acids into butyric acid through acid-producing bacteria to obtain a post-fermentation solution; electrolyzing the post-fermentation solution, utilizing electroactive hydrogen-producing bacteria for extracellular electron transfer to convert residual organic matter in the solution into hydrogen gas to obtain crude hydrogen, which is then purified to obtain hydrogen gas. This invention solves the problems of low utilization rate of organic wastewater, inhibition of hydrogen production by volatile acids, and the impact of environmental parameter fluctuations on yield in existing processes.

Description

Technical Field

[0001] This invention relates to the field of hydrogen production through fermentation, and in particular to a method for producing hydrogen through dark fermentation of organic wastewater. Background Technology

[0002] Organic wastewater, as one of the major pollutants in industrial and agricultural production and daily life, is characterized by high organic matter concentration, complex composition, difficulty in treatment, and large discharge volume. Its harmless treatment and resource utilization have become a key research focus. Converting organic matter in organic wastewater into hydrogen through biological fermentation can achieve the dual goals of pollution control and energy production. This not only alleviates the environmental pressure caused by organic wastewater discharge but also generates clean and renewable energy, aligning with the current trend of green and low-carbon development and becoming one of the main directions for the resource utilization of organic wastewater.

[0003] However, in practical applications, existing dark fermentation hydrogen production processes for organic wastewater consistently fail to achieve ideal hydrogen yields. The main reasons are: insufficient pretreatment of the organic wastewater prevents efficient utilization of recalcitrant organic matter by hydrogen-producing bacteria, resulting in low substrate conversion rates and a significant amount of organic matter failing to convert into hydrogen; the natural generation of volatile acids during fermentation, which, upon accumulation, inhibits the metabolic activity of hydrogen-producing bacteria, leading to slow bacterial growth, reduced hydrogen production capacity, and consequently lower overall hydrogen production efficiency; fluctuations in environmental parameters of the fermentation system (such as pH and dissolved oxygen) further disrupt the suitable growth environment for hydrogen-producing bacteria, causing instability in the hydrogen production process and significant fluctuations in hydrogen yield. Furthermore, the incomplete conversion of residual organic matter in the fermentation liquid wastes energy and indirectly reduces the hydrogen output per unit volume of organic wastewater, making it difficult to meet the demands of large-scale industrial hydrogen production. Summary of the Invention

[0004] In order to overcome the shortcomings of the existing technology, the purpose of this invention is to provide a method for hydrogen production by dark fermentation of organic wastewater, which solves the problems of low utilization rate of organic wastewater, inhibition of hydrogen production by volatile acids, and impact of environmental parameter fluctuations on yield in the existing process, improves the resource utilization efficiency of organic wastewater, reduces resource waste, and achieves stable and efficient hydrogen production.

[0005] To achieve the above objectives, the present invention provides a method for hydrogen production through dark fermentation of organic wastewater, comprising the following steps: Pretreatment steps: Organic wastewater, biochar loaded with metal nanoparticles, and domesticated butyric acid-producing mixed bacteria are mixed and subjected to micro-electrolysis and biological activation treatment to obtain pretreated liquid. The fermentation process involves: first, subjecting the pretreated liquid to hydrogen-producing phase fermentation and adding an electron mediator to obtain a fermentation broth containing volatile acids; then, subjecting the fermentation broth to desuppressive phase treatment and using adsorption materials to adsorb the volatile acids, while simultaneously using acid-producing bacteria to convert some of the adsorbed volatile acids into butyric acid, thus obtaining the fermented liquid. Electrolytic hydrogen production step: The fermented liquid is electrolyzed to convert the residual organic matter in the liquid into hydrogen gas by using electroactive hydrogen-producing bacteria to transfer extracellular electrons, thus obtaining crude hydrogen. Hydrogen purification step: The crude hydrogen is purified to obtain hydrogen gas.

[0006] Preferably, in the biochar loaded with metal nanoparticles, the metal nanoparticles are one or more of Fe3O4 nanoparticles, ZnO nanoparticles, and TiO2 nanoparticles, and their loading is 8% to 12% of the mass of the biochar; the concentration of the biochar is 200 to 350 mg / L, and the time for the micro-electrolysis and biological activation treatment is 1.5 to 2.5 h.

[0007] Preferably, the butyric acid-producing mixed bacterial community includes one or more of Clostridium, Vibrio butyricum, and Bifidobacterium, and its concentration is not less than 10. 8 CFU / mL.

[0008] Preferably, the temperature of the hydrogen-producing fermentation treatment is 38~42℃, the pH is 5.2~5.8, and the hydraulic retention time is 3~5h; the electron mediator is one or more of neutral red, methylene blue, and flavin, and the concentration is 0.5~1.0mmol / L.

[0009] Preferably, the temperature of the desuppression phase treatment is 32~36℃, and the pH is 6.0~6.5; the adsorbent material is one or more of modified zeolite, activated carbon, and diatomaceous earth.

[0010] Preferably, in the desuppression phase treatment, butyric acid with a concentration not exceeding 500 mg / L is refluxed into the hydrogen-producing phase fermentation process.

[0011] Preferably, the control conditions for the electrolysis treatment are: electrolysis voltage 0.6~0.8V, electrolysis reaction time 2.5~3.5h; the electrolysis treatment uses one or more of carbon cloth-loaded hydrogen-producing bacteria, graphite electrode, and carbon paper electrode as cathode, and one or more of titanium-based oxide electrode, platinum electrode, and graphite electrode as anode.

[0012] Preferably, hollow fiber membrane separation is used in the hydrogen purification step, and the pore size of the hollow fiber membrane is 0.01~0.1μm.

[0013] Preferably, in at least one of the pretreatment step, the partitioned fermentation step, and the electrolysis hydrogen production step, the pH value of the system is adjusted by adding alkali solution, and the dissolved oxygen concentration is controlled to not exceed 0.5 mg / L throughout the process.

[0014] Preferably, the alkaline solution is an aqueous solution of one or more of NaHCO3, Na2CO3, and KHCO3.

[0015] Compared with the prior art, the present invention discloses at least the following technical effects: (1) This invention mixes organic wastewater with biochar loaded with metal nanoparticles and domesticated butyric acid-type hydrogen-producing mixed bacteria. It uses micro-electrolysis to efficiently degrade the recalcitrant organic matter in the wastewater and convert it into a substrate that can be utilized by the hydrogen-producing bacteria. At the same time, the biochar acts as a carrier to fix the hydrogen-producing bacteria and enhance their activity. Combined with domesticated specific hydrogen-producing bacteria, the substrate conversion rate of organic wastewater is greatly improved, the waste of organic matter is reduced, and the problem of low substrate utilization rate in existing processes is solved from the root.

[0016] (2) By setting up a partitioned fermentation mode, the hydrogen-producing phase and the de-inhibition phase are separated, and the volatile acids generated during the fermentation process are adsorbed and removed. At the same time, some of the volatile acids are converted into butyric acid by acid-producing bacteria, and the butyric acid reflux concentration is controlled to avoid excessive accumulation of volatile acids that inhibits the hydrogen-producing bacteria. This effectively alleviates the fermentation inhibition problem, significantly improves the hydrogen yield, and solves the problem of low yield caused by volatile acid inhibition in the existing process.

[0017] (3) By setting up an independent pH monitoring and alkali supplementation unit, this invention adjusts the environmental parameters of each step of pretreatment, fermentation and electrolysis, and controls the dissolved oxygen concentration to stabilize the growth environment of hydrogen-producing bacteria, avoid the impact of environmental parameter fluctuations on the hydrogen production process, ensure the stable progress of the hydrogen production process, reduce the fluctuation range of hydrogen yield, and solve the problem of unstable hydrogen production process in existing processes.

[0018] (4) The present invention adds an electrolysis hydrogen production step after partitioned fermentation, and uses electroactive hydrogen-producing bacteria to realize extracellular electron transfer, fully converting the residual organic matter in the fermentation liquid, further tapping the energy potential of organic wastewater, increasing the hydrogen production per unit volume of organic wastewater, adapting to the needs of industrial-scale production, and solving the problems of residual organic matter waste and insufficient total hydrogen production in the existing process. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the 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.

[0020] Figure 1 This is a flowchart of a method for hydrogen production by dark fermentation of organic wastewater according to the present invention; Figure 2 This is a comparison chart of substrate conversion rate curves provided for embodiments and comparative examples of the present invention; Figure 3 The bar chart showing the hydrogen production per unit wastewater in the embodiments and comparative examples of the present invention is provided below. Figure 4 This is a comparison chart of the volatile acid inhibition rate curves provided in the embodiments and comparative examples of the present invention; Figure 5 The bar chart shows the hydrogen purity of the embodiments and comparative examples of the present invention. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0023] like Figure 1 As shown, this invention provides a method for hydrogen production through dark fermentation of organic wastewater, comprising the following steps: S1. Pretreatment step: Mix organic wastewater, biochar loaded with metal nanoparticles, and domesticated butyric acid-producing mixed bacteria, and perform micro-electrolysis and biological activation treatment to obtain pretreated liquid.

[0024] Specifically, in the biochar loaded with metal nanoparticles, the metal nanoparticles are one or more of Fe3O4 nanoparticles, ZnO nanoparticles, and TiO2 nanoparticles, with a loading of 8% to 12% of the biochar mass, and the biochar dosage is 200 to 350 mg / L. The butyric acid-type hydrogen-producing mixed bacterial community includes one or more of Clostridium, Vibrio butyricum, and Bifidobacterium, with a community concentration of not less than 10. 8CFU / mL; the microelectrolysis and bioactivation treatment time is 1.5~2.5h. Metal nanoparticles enhance the conductivity of biochar and improve the efficiency of the microelectrolysis reaction. Microelectrolysis breaks the chemical bonds of recalcitrant organic matter, degrading it into small molecule substrates that are easily utilized by hydrogen-producing bacteria. Simultaneously, the high specific surface area of ​​biochar provides stable attachment sites for hydrogen-producing bacteria, reducing bacterial loss. Combined with domesticated butyric acid-producing mixed bacteria, the utilization efficiency of the substrate by the bacteria can be significantly improved, activating the hydrogen-producing bacteria and thus increasing the substrate conversion rate in subsequent hydrogen production processes. This solves the problems of insufficient pretreatment and low utilization rate of recalcitrant organic matter in existing processes.

[0025] S2, Partitioned Fermentation Step: The pretreated liquid is first subjected to hydrogen-producing phase fermentation treatment, and an electron mediator is added to obtain a fermentation broth containing volatile acids; then the fermentation broth is subjected to de-inhibition phase treatment, and the volatile acids are adsorbed using adsorption materials. At the same time, some of the adsorbed volatile acids are converted into butyric acid by acid-producing bacteria to obtain the fermented liquid.

[0026] Specifically, the temperature of the hydrogen-producing phase fermentation treatment is 38~42℃, the pH is 5.2~5.8, and the hydraulic retention time is 3~5h; the electron mediator is one or more of neutral red, methylene blue, and flavin, with an addition concentration of 0.5~1.0mmol / L; the temperature of the desuppression phase treatment is 32~36℃, the pH is 6.0~6.5, and the adsorbent is one or more of modified zeolite, activated carbon, and diatomaceous earth; in the desuppression phase treatment, butyric acid with a concentration not exceeding 500mg / L is refluxed to the hydrogen-producing phase fermentation process, while butyric acid with a concentration higher than this remains in the desuppression phase. Among them, the temperature and pH parameters of the hydrogen production phase are the optimal growth and metabolic conditions for butyric acid-producing hydrogen-producing bacteria, which can maximize the activation of hydrogen-producing enzyme activity. The electron mediator can accelerate electron transfer in the hydrogen production process, promote the efficient hydrogen production reaction, and improve the hydrogen production rate. The parameter settings of the de-inhibition phase can be adapted to the adsorption performance of the adsorbent material and the metabolic activity of the acid-producing bacteria. The adsorbent material can quickly adsorb volatile acids, avoiding their accumulation in the hydrogen production phase and inhibiting the hydrogen-producing bacteria. The acid-producing bacteria convert some of the volatile acids into butyric acid and control the reflux concentration, which not only realizes the resource utilization of volatile acids, but also further increases the supply of hydrogen production substrate, effectively alleviates fermentation inhibition, and improves the overall hydrogen production efficiency.

[0027] S3. Electrolysis hydrogen production step: The fermented liquid is electrolyzed to convert the residual organic matter in the liquid into hydrogen gas by using electroactive hydrogen-producing bacteria to transfer extracellular electrons, thus obtaining crude hydrogen.

[0028] Specifically, the control conditions for electrolysis are as follows: electrolysis voltage 0.6~0.8V, electrolysis reaction time 2.5~3.5h; the electrolysis process uses one or more of the following as cathodes: carbon cloth-loaded hydrogen-producing bacteria, graphite electrode, and carbon paper electrode; and one or more of the following as anodes: titanium-based oxide electrode, platinum electrode, and graphite electrode; during electrolysis, the redox potential of the system is maintained to ensure efficient extracellular electron transfer. The electrolysis voltage in this step avoids damage to the hydrogen-producing bacteria due to excessive voltage, while providing sufficient power for extracellular electron transfer. The matched electrode materials reduce electron transfer resistance and improve electron transfer efficiency. Electroactive hydrogen-producing bacteria can transfer electrons from residual organic matter to the electrode surface through extracellular electron transfer, achieving complete oxidation and decomposition of residual organic matter and conversion into hydrogen gas, further tapping the energy potential of organic wastewater, increasing total hydrogen production, and reducing resource waste.

[0029] S4. Hydrogen purification step: The crude hydrogen is purified to obtain hydrogen gas.

[0030] Specifically, the hydrogen purification step employs hollow fiber membrane separation, where the pore size of the hollow fiber membrane is 0.01~0.1μm. This method can purify crude hydrogen to meet industrial standards. Simultaneously, in at least one of the pretreatment, partitioned fermentation, and electrolysis hydrogen production steps, the pH of the system is adjusted by adding an alkali solution. The alkali solution is an aqueous solution of one or more of NaHCO3, Na2CO3, and KHCO3, and the dissolved oxygen concentration is controlled throughout the process to not exceed 0.5mg / L, ensuring the activity of the hydrogen-producing bacteria. The pore size of the hollow fiber membrane can trap impurities such as moisture and carbon dioxide in the crude hydrogen, achieving efficient hydrogen purification and ensuring that the product hydrogen meets industrial application requirements. The choice of alkali solution allows for gentle pH adjustment, preventing sudden pH changes from damaging the metabolic activity of the hydrogen-producing bacteria. Controlling the dissolved oxygen concentration throughout the process maintains an anaerobic growth environment for the hydrogen-producing bacteria, preventing oxygen from inhibiting the hydrogen production reaction, ensuring the entire hydrogen production process is stable and efficient, and reducing fluctuations in the hydrogen production rate.

[0031] The present invention will be further described in detail below with reference to specific embodiments. The raw materials and equipment used in the embodiments are all conventional commercially available products, and the operations not specifically described are all conventional operations of the prior art.

[0032] Example 1 This embodiment provides a method for hydrogen production from organic wastewater through dark fermentation, including the following steps: Pretreatment steps: Take organic wastewater with a COD concentration of 5000 mg / L, and mix it with biochar loaded with Fe3O4 nanoparticles (Fe3O4 loading of 10%, biochar concentration of 280 mg / L) and a domesticated butyric acid-producing mixed bacterial community (including Clostridium and Vibrio butyricum, bacterial community concentration of 10). 8The mixture (CFU / mL) was subjected to micro-electrolysis and bio-activation for 2.0 h to obtain a pretreated solution. Fermentation steps: The pretreated liquid is fed into the hydrogen-producing phase, and the temperature of the hydrogen-producing phase is controlled at 40℃, pH at 5.5, and hydraulic retention time at 4h. Neutral red is added as an electron mediator (concentration of 0.8mmol / L) to obtain a fermentation broth containing volatile acids. The fermentation broth is then fed into the de-suppression phase, and the temperature of the de-suppression phase is controlled at 34℃ and pH at 6.2. Activated carbon is filled as an adsorbent material, and acid-producing bacteria are inoculated. The butyric acid produced at a concentration of 400mg / L is refluxed to the hydrogen-producing phase to obtain the post-fermentation liquid. Electrolytic hydrogen production steps: The fermented liquid is fed into an electrolysis device, the electrolysis voltage is controlled at 0.7V, the electrolysis reaction time is 3.0h, the hydrogen-producing bacteria loaded on carbon cloth are used as the cathode and the graphite electrode is used as the anode. The electroactive hydrogen-producing bacteria are used to transfer extracellular electrons to convert the residual organic matter in the liquid into hydrogen gas, and crude hydrogen is obtained. Hydrogen purification steps: Crude hydrogen is purified by hollow fiber membrane separation. The hollow fiber membrane has a pore size of 0.05 μm to obtain hydrogen gas.

[0033] Throughout the pretreatment, fermentation, and hydrogen electrolysis processes, the pH of the system was adjusted by adding NaHCO3 aqueous solution to control the dissolved oxygen concentration to not exceed 0.5 mg / L.

[0034] Example 2 This embodiment provides a method for hydrogen production from organic wastewater through dark fermentation, including the following steps: Pretreatment steps: Take organic wastewater with a COD concentration of 5500 mg / L, and mix it with biochar loaded with ZnO nanoparticles (ZnO loading of 8%, biochar concentration of 200 mg / L), and a domesticated butyric acid-producing mixed bacterial community (containing Clostridium and Bifidobacterium, with a community concentration of 1.0 × 10⁻⁶). 8 The mixture (CFU / mL) was subjected to micro-electrolysis and bio-activation for 1.5 hours to obtain a pretreated solution. Fermentation steps: The pretreated liquid is fed into the hydrogen-producing phase, and the temperature of the hydrogen-producing phase is controlled at 38℃, pH at 5.2, and hydraulic retention time at 3h. Methylene blue is added as an electron mediator (concentration of 0.5mmol / L) to obtain a fermentation broth containing volatile acids. The fermentation broth is then fed into the de-suppression phase, and the temperature of the de-suppression phase is controlled at 32℃ and pH at 6.0. Modified zeolite is filled as an adsorbent material, and acid-producing bacteria are inoculated. The butyric acid produced at a concentration of 350mg / L is refluxed to the hydrogen-producing phase to obtain the post-fermentation liquid. Electrolytic hydrogen production steps: The fermented liquid is fed into an electrolysis device, the electrolysis voltage is controlled at 0.6V, the electrolysis reaction time is 2.5h, a graphite electrode is used as the cathode and a titanium oxide electrode is used as the anode. The electroactive hydrogen-producing bacteria are used to transfer extracellular electrons to convert the residual organic matter in the liquid into hydrogen gas, and crude hydrogen is obtained. Hydrogen purification steps: Crude hydrogen is purified by hollow fiber membrane separation. The hollow fiber membrane has a pore size of 0.01 μm to obtain hydrogen gas.

[0035] Throughout the pretreatment and partitioned fermentation processes, the pH of the system was adjusted by adding Na2CO3 aqueous solution to control the dissolved oxygen concentration to not exceed 0.5 mg / L.

[0036] Example 3 This embodiment provides a method for hydrogen production from organic wastewater through dark fermentation, including the following steps: Pretreatment steps: Take organic wastewater with a COD concentration of 6000 mg / L, and mix it with biochar loaded with TiO2 nanoparticles (TiO2 loading of 12%, biochar concentration of 350 mg / L), and a domesticated butyric acid-producing mixed bacterial community (containing Vibrio butyricum and Bifidobacterium, with a community concentration of 1.2 × 10⁻⁶). 8 The mixture (CFU / mL) was subjected to micro-electrolysis and bio-activation for 2.5 hours to obtain a pretreated solution. Fermentation steps: The pretreated liquid was fed into the hydrogen-producing phase, and the temperature of the hydrogen-producing phase was controlled at 42℃, pH at 5.8, and hydraulic retention time at 5h. Flavin was added as an electron mediator (concentration of 1.0 mmol / L) to obtain a fermentation broth containing volatile acids. The fermentation broth was then fed into the de-suppression phase, and the temperature of the de-suppression phase was controlled at 36℃ and pH at 6.5. Diatomaceous earth was filled as an adsorbent material, and acid-producing bacteria were inoculated. The butyric acid produced at a concentration of 450 mg / L was refluxed into the hydrogen-producing phase to obtain the fermented liquid. Electrolytic hydrogen production steps: The fermented liquid is fed into an electrolysis device, the electrolysis voltage is controlled at 0.8V, the electrolysis reaction time is 3.5h, carbon paper electrode is used as cathode and platinum electrode is used as anode, and the extracellular electron transfer of electroactive hydrogen-producing bacteria is used to convert the residual organic matter in the liquid into hydrogen gas to obtain crude hydrogen. Hydrogen purification steps: Crude hydrogen is purified by hollow fiber membrane separation. The hollow fiber membrane has a pore size of 0.1 μm to obtain hydrogen gas.

[0037] Throughout the electrolysis hydrogen production process, the pH value of the system is adjusted by adding KHCO3 aqueous solution to control the dissolved oxygen concentration to not exceed 0.5 mg / L.

[0038] Example 4 This embodiment provides a method for hydrogen production from organic wastewater through dark fermentation, including the following steps: Pretreatment steps: Take organic wastewater with a COD concentration of 5200 mg / L and mix it with biochar loaded with Fe3O4+ZnO composite nanoparticles (composite loading of 9%, Fe3O4 to ZnO mass ratio of 1:1, biochar concentration of 250 mg / L) and domesticated butyric acid-producing hydrogen-producing mixed bacteria (including Clostridium, Vibrio butyricum, and Bifidobacterium, with a bacterial concentration of 1.1 × 10⁻⁶). 8 The mixture (CFU / mL) was subjected to micro-electrolysis and bio-activation for 2.0 h to obtain a pretreated solution. Fermentation steps: The pretreated liquid was transferred to the hydrogen-producing phase, and the temperature of the hydrogen-producing phase was controlled at 39℃, pH at 5.4, and hydraulic retention time at 3.5h. Neutral red + methylene blue composite electron mediator (total concentration of 0.7mmol / L, mass ratio of 1:1) was added, and fermentation was carried out to obtain a fermentation broth containing volatile acids. The fermentation broth was then transferred to the de-suppression phase, and the temperature of the de-suppression phase was controlled at 33℃ and pH at 6.1. Activated carbon + modified zeolite composite adsorbent material (mass ratio of 2:1) was filled in, and acid-producing bacteria were inoculated. The butyric acid produced at a concentration of 420mg / L was refluxed to the hydrogen-producing phase to obtain the post-fermentation liquid. Electrolytic hydrogen production steps: The fermented liquid is fed into an electrolysis device, the electrolysis voltage is controlled at 0.7V, the electrolysis reaction time is 3.0h, the hydrogen-producing bacteria loaded on carbon cloth are used as the cathode and the titanium-based oxide electrode is used as the anode. The electroactive hydrogen-producing bacteria are used to transfer extracellular electrons to convert the residual organic matter in the liquid into hydrogen gas, and crude hydrogen is obtained. Hydrogen purification steps: Crude hydrogen is purified by hollow fiber membrane separation. The hollow fiber membrane has a pore size of 0.06 μm to obtain hydrogen gas.

[0039] Throughout the pretreatment, fermentation, and hydrogen electrolysis processes, the pH of the system was adjusted by adding a NaHCO3 + Na2CO3 composite alkaline solution (with a concentration ratio of 1:1) to control the dissolved oxygen concentration to not exceed 0.5 mg / L.

[0040] Example 5 This embodiment provides a method for hydrogen production from organic wastewater through dark fermentation, including the following steps: Pretreatment steps: Take organic wastewater with a COD concentration of 5800 mg / L, and mix it with biochar loaded with TiO2+Fe3O4 composite nanoparticles (composite loading of 11%, TiO2 to Fe3O4 mass ratio of 2:1, biochar concentration of 300 mg / L), and a domesticated butyric acid-producing mixed bacterial community (including Clostridium and Vibrio butyricum, bacterial community concentration of 1.3 × 10⁻⁶). 8The mixture (CFU / mL) was subjected to micro-electrolysis and bio-activation for 2.2 hours to obtain a pretreated solution. Fermentation steps: The pretreated liquid was transferred to the hydrogen-producing phase, and the temperature of the hydrogen-producing phase was controlled at 41℃, pH at 5.7, and hydraulic retention time at 4.5h. A flavin + neutral red composite electron mediator (total concentration of 0.9mmol / L, mass ratio of 3:2) was added, and fermentation was carried out to obtain a fermentation broth containing volatile acids. The fermentation broth was then transferred to the de-suppression phase, and the temperature of the de-suppression phase was controlled at 35℃ and pH at 6.4. A diatomaceous earth + activated carbon composite adsorbent material (mass ratio of 1:2) was filled in, and acid-producing bacteria were inoculated. The butyric acid produced at a concentration of 480mg / L was refluxed to the hydrogen-producing phase to obtain the post-fermentation liquid. Electrolysis hydrogen production steps: The fermented liquid is fed into the electrolysis device, the electrolysis voltage is controlled at 0.75V, the electrolysis reaction time is 3.2h, a graphite + carbon paper composite electrode is used as the cathode and a graphite electrode is used as the anode, and the extracellular electron transfer of the electroactive hydrogen-producing bacteria is used to convert the residual organic matter in the liquid into hydrogen gas to obtain crude hydrogen. Hydrogen purification steps: Crude hydrogen is purified by hollow fiber membrane separation. The hollow fiber membrane has a pore size of 0.08 μm to obtain hydrogen gas.

[0041] Throughout the pretreatment and electrolysis hydrogen production steps, the pH value of the system is adjusted by adding NaHCO3+KHCO3 composite alkaline solution (concentration ratio of the two is 2:1) to control the dissolved oxygen concentration to not exceed 0.5 mg / L.

[0042] Comparative Example 1 This comparative example provides a method for hydrogen production from organic wastewater through dark fermentation. The difference from Example 1 is that it does not add biochar loaded with metal nanoparticles, but uses unacclimated common anaerobic bacteria (bacterial concentration 10). 8 The CFU / mL ratio was used to replace the domesticated butyric acid-producing mixed bacterial community, and the remaining process parameters were completely consistent with those in Example 1.

[0043] Comparative Example 2 This comparative example provides a method for hydrogen production by dark fermentation of organic wastewater. Compared with Example 1, the difference is that no electron mediator is added, no partitioned fermentation is set up, and a single fermenter is used for one-step fermentation (fermentation temperature 37℃, pH 5.5, hydraulic retention time 4h). The remaining process parameters are completely consistent with those of Example 1.

[0044] Comparative Example 3 This comparative example provides a method for hydrogen production by dark fermentation of organic wastewater. The difference from Example 1 is that the butyric acid produced by the desuppression phase is not refluxed to the hydrogen production phase, but is entirely retained in the desuppression phase. The other process parameters are completely consistent with those of Example 1.

[0045] Comparative Example 4 This comparative example provides a method for hydrogen production by dark fermentation of organic wastewater. Compared with Example 1, the difference is that the electrolysis hydrogen production step is omitted, and the fermented liquid is directly purified into hydrogen. The remaining process parameters are completely consistent with those of Example 1.

[0046] Comparative Example 5 This comparative example provides a method for hydrogen production from conventional organic wastewater via dark fermentation. The specific steps are as follows: Take organic wastewater with a COD concentration of 5000 mg / L and directly inoculate it with common hydrogen-producing bacteria (bacterial concentration 10). 8 The hydrogen was subjected to one-step dark fermentation (fermentation temperature 37℃, pH 5.5, hydraulic retention time 4h) without the addition of electron mediators, micro-electrolysis pretreatment, or setting of a desuppression phase. After fermentation, crude hydrogen was obtained and purified by conventional pressure swing adsorption. The dissolved oxygen concentration was not controlled throughout the process (the natural dissolved oxygen concentration was about 1.2mg / L), and no alkali solution was added to adjust the pH.

[0047] The hydrogen production effects of the above embodiments and comparative examples were tested, and the test indicators included substrate conversion rate (the proportion of organic wastewater COD converted into usable substrate), hydrogen production per unit wastewater, volatile acid inhibition rate (the lower the value, the weaker the inhibition effect), and hydrogen purity. Figure 2 , Figure 3 , Figure 4 and Figure 5 As shown, the substrate conversion rate, hydrogen production per unit wastewater, and hydrogen purity of each embodiment of the present invention are significantly higher than those of the comparative examples, while the volatile acid inhibition rate is significantly lower than that of the comparative examples; Figures 2 to 5 The data shown is summarized in Table 1.

[0048] Table 1 Comparison of test results data

[0049] As shown in Table 1, Examples 1 to 5 provided by this invention achieve substrate conversion rates of 78.5% to 83.5%, hydrogen production per unit wastewater of 115 to 150 mL / L, volatile acid inhibition rates of only 6.0% to 8.5%, and hydrogen purity of 99.2% to 99.5%. This is attributed to the combined application of multiple technologies, including metal nanoparticle-modified biochar micro-electrolysis pretreatment activation, specific domestication of butyric acid-producing mixed bacterial communities, electron mediators accelerating extracellular electron transfer, partitioned fermentation coupled with butyric acid reflux desuppression, and electrolysis-enhanced deep hydrogen production. Compared with the comparative examples, this invention effectively improves many defects in traditional dark fermentation processes, such as low substrate utilization rate of organic wastewater, accumulation of volatile acids inhibiting hydrogen production, poor stability of the fermentation system, waste of residual organic matter, and insufficient gas purity. It significantly improves the resource utilization level of organic wastewater and achieves stable, efficient, and high-purity dark fermentation hydrogen production in an organic wastewater system.

[0050] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0051] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for hydrogen production through dark fermentation of organic wastewater, characterized in that, Includes the following steps: Pretreatment steps: Organic wastewater, biochar loaded with metal nanoparticles, and domesticated butyric acid-producing mixed bacteria are mixed and subjected to micro-electrolysis and biological activation treatment to obtain pretreated liquid. The fermentation process involves: first, subjecting the pretreated liquid to hydrogen-producing phase fermentation and adding an electron mediator to obtain a fermentation broth containing volatile acids; then, subjecting the fermentation broth to desuppressive phase treatment and using adsorption materials to adsorb the volatile acids, while simultaneously using acid-producing bacteria to convert some of the adsorbed volatile acids into butyric acid, thus obtaining the fermented liquid. Electrolytic hydrogen production step: The fermented liquid is electrolyzed to convert the residual organic matter in the liquid into hydrogen gas by using electroactive hydrogen-producing bacteria to transfer extracellular electrons, thus obtaining crude hydrogen. Hydrogen purification step: The crude hydrogen is purified to obtain hydrogen gas.

2. The method according to claim 1, characterized in that, In the biochar loaded with metal nanoparticles, the metal nanoparticles are one or more of Fe3O4 nanoparticles, ZnO nanoparticles, and TiO2 nanoparticles, and their loading is 8% to 12% of the mass of the biochar; the concentration of the biochar is 200 to 350 mg / L, and the time for the micro-electrolysis and biological activation treatment is 1.5 to 2.5 h.

3. The method according to claim 1, characterized in that, The butyric acid-producing mixed bacterial community includes one or more of the genera *Clostridium*, *Vibrio butyricum*, and *Bifidobacterium*, with a concentration of not less than 10. 8 CFU / mL.

4. The method according to claim 1, characterized in that, The hydrogen-producing fermentation treatment is carried out at a temperature of 38-42℃, a pH of 5.2-5.8, and a hydraulic retention time of 3-5 hours. The electron mediator is one or more of neutral red, methylene blue, and flavin, and the concentration is 0.5-1.0 mmol / L.

5. The method according to claim 1, characterized in that, The temperature for the desuppression phase treatment is 32~36℃, and the pH is 6.0~6.5; the adsorbent material is one or more of modified zeolite, activated carbon, and diatomaceous earth.

6. The method according to claim 5, characterized in that, In the desuppression phase treatment, butyric acid with a concentration not exceeding 500 mg / L is refluxed into the hydrogen-producing phase fermentation process.

7. The method according to claim 1, characterized in that, The control conditions for the electrolysis treatment are: electrolysis voltage 0.6~0.8V, electrolysis reaction time 2.5~3.5h; the electrolysis treatment uses one or more of the following as cathodes: carbon cloth loaded hydrogen-producing bacteria, graphite electrode, and carbon paper electrode, and one or more of the following as anodes: titanium oxide electrode, platinum electrode, and graphite electrode.

8. The method according to claim 1, characterized in that, The hydrogen purification step employs hollow fiber membrane separation, wherein the pore size of the hollow fiber membrane is 0.01~0.1μm.

9. The method according to claim 1, characterized in that, In at least one of the pretreatment step, the partitioned fermentation step, and the electrolysis hydrogen production step, the pH value of the system is adjusted by adding alkali solution, and the dissolved oxygen concentration is controlled to not exceed 0.5 mg / L throughout the process.

10. The method according to claim 9, characterized in that, The alkaline solution is an aqueous solution of one or more of NaHCO3, Na2CO3, and KHCO3.

Images