Method for enhancing hydrogen production by anaerobic fermentation of sludge
Through the pretreatment method of free nitrite acid and citric acid, the problem of large energy and chemical consumption during the pretreatment process before hydrogen production of sludge fermentation is solved, and high hydrogen yield and environmentally friendly anaerobic fermentation effect is achieved.
Patent Information
- Application Number
- CN202411766729.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-04
- Publication Date
- 2025-02-11
AI Technical Summary
During the pretreatment process of sludge before fermentation and hydrogen production, there is high energy and consumption of chemicals, resulting in environmental pollution.
Free nitrite and citric acid are used for pretreatment, and oxygen is removed by adjusting the pH value and filling nitrogen to form an environment suitable for anaerobic fermentation.
It enhances the inhibitory effect of hydrogen-consuming microorganisms, destroys the extracellular polymers and cells themselves of sludge microorganisms, accelerates the release of intracellular substances, provides a reaction substrate for fermenting hydrogen-producing microorganisms, increases hydrogen production, and reduces the Environmental pollution.
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Figure BDA0005169143260000031
Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of anaerobic fermentation, and in particular relates to a method for strengthening sludge anaerobic fermentation to produce hydrogen. Background Art
[0002] As a by-product of the sewage treatment process, residual sludge has the characteristics of large capacity, instability, and easy corruption, which can easily cause secondary pollution. But at the same time, sludge is an invisible resource rich in organic carbon, which contains a large amount of protein, polysaccharides, fat and other organic matter, the content of which can reach 40-75% of the dry weight of the sludge.
[0003] Anaerobic digestion can simultaneously achieve sludge organic matter stabilization, sludge reduction and biomass energy recovery, and is one of the mainstream technologies for sewage treatment plants to achieve synergistic efficiency of pollution reduction and carbon reduction. Anaerobic digestion includes three stages: hydrolysis and fermentation, hydrogen production, acetic acid production and methane production. Hydrogen is an important intermediate product in the anaerobic digestion process of sludge and is a clean and high-calorie (142.35kJ / g) energy source. However, during the anaerobic digestion process, the hydrogen produced will be quickly consumed by hydrogen-consuming microorganisms such as homoacetogenic bacteria and methanogenic bacteria. In addition, due to the encapsulation of sludge extracellular polymers and the semi-rigid structure of microbial cells, the sludge is difficult to disintegrate, thereby limiting the sludge hydrolysis and acidification process. Therefore, before fermentation and hydrogen production, the sludge must be pretreated physically, chemically or biologically to destroy the cell structure, accelerate the dissolution of intracellular substances, and hydrogen-producing bacteria can also be screened. However, the pretreatment process often involves high energy and chemical consumption, which is easy to bring new environmental problems while treating sludge. Therefore, it is urgent to invent a pretreatment method that is environmentally friendly, stable in operation and has a large hydrogen production. Summary of the invention
[0004] The purpose of the present invention is to provide a method for enhancing anaerobic fermentation of sludge to produce hydrogen, which effectively solves the problem of environmental pollution caused by high energy and chemical consumption in the pretreatment process of sludge before fermentation to produce hydrogen.
[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is:
[0006] A method for enhancing anaerobic fermentation of sludge to produce hydrogen comprises the following steps: S1, screening the sludge, refrigerating and standing it, discarding the supernatant and obtaining a sludge sample.
[0007] S2. After the sludge sample is restored to room temperature, it is placed in a glass reactor for pretreatment. Sodium nitrite is added to the glass reactor containing the sludge sample, and the pH is adjusted to 5.5±0.1 with citric acid. The concentration of free nitrite in the glass reactor is controlled to be 0.73-1.29 mg / L, and the pretreatment time is 4-5 h.
[0008] S3. After the pretreatment is completed, nitrogen is charged into the glass reactor of step S2 to remove oxygen in the glass reactor.
[0009] S4. After sealing the glass reactor, place it in an air bath constant temperature shaking incubator for anaerobic fermentation until no hydrogen is generated.
[0010] Furthermore, in step S4, the temperature of the shaking table is 35±1° C. and the rotation speed is 120 rpm.
[0011] Furthermore, in step S3, the glass reactor is filled with nitrogen for 5 to 10 minutes.
[0012] Furthermore, in step S1, the refrigeration temperature is 4°C and the standing time is 12 to 24 hours.
[0013] Furthermore, in step S2, the initial concentration of sodium nitrite in the glass reactor is 180 mg / L, and the cumulative dosage of citric acid is 215±10 mg.
[0014] Compared with the prior art, the beneficial technical effects of the present invention are:
[0015] (1) The present invention utilizes free nitrite combined with citric acid to pretreat sludge, which can enhance the inhibitory effect on hydrogen-consuming microorganisms in the anaerobic fermentation system of sludge, enhance the destructive effect on the extracellular polymers and cells of sludge microorganisms, and thus accelerate the release of sludge intracellular substances, providing reaction substrates for fermentation hydrogen-producing microorganisms.
[0016] (2) The present invention uses citric acid to replace traditional inorganic acids (such as hydrochloric acid) for acid-base adjustment. First, it reduces the production of inorganic salts and does not cause secondary pollution to the sludge, which is environmentally friendly. Second, citric acid itself serves as a carbon source, providing more reaction substrates for fermentation and hydrogen-producing microorganisms. Finally, the addition of citric acid improves the sludge C / N ratio, eliminates the nitrogen load caused by free nitrous acid, and helps the sludge fermentation to produce hydrogen. DETAILED DESCRIPTION
[0017] Example 1: A method for enhancing anaerobic fermentation of sludge to produce hydrogen, comprising the following steps: S1, sieving the sludge and standing it at 4°C for 12 to 24 hours, discarding the supernatant to obtain a sludge sample. The total solid TS of the sludge sample is 21.8±0.2 g / L, the volatile solid VS is 9.5±0.2 g / L, and the pH is 7.1±0.1.
[0018] S2. After the sludge sample is restored to room temperature (18-22° C.), it is placed in a glass reactor as a substrate for anaerobic fermentation to produce hydrogen. Then, the sludge sample in the glass reactor is pretreated for 4-5 hours.
[0019] In this embodiment, the pretreatment process is: add an appropriate amount of 45g / L sodium nitrite standard stock solution to the glass reactor containing the sludge sample, so that the initial concentration of sodium nitrite in the reaction system is 180mg / L, and then use citric acid to adjust the pH to 5.5±0.1, and control the concentration of free nitrous acid in the glass reactor to 0.73-1.29mg / L (temperature and pH will affect the concentration of free nitrous acid). In this embodiment, the cumulative amount of citric acid added is 215±10mg.
[0020] S3. After the pretreatment, high-purity nitrogen (purity 99.999%) is charged into the reaction system for 5 to 10 minutes, thereby removing oxygen in the glass reactor and providing an anaerobic environment for fermentation.
[0021] S4. After sealing the glass reactor, place it in an air bath constant temperature shaking incubator at 35±1°C and 120 rpm for anaerobic fermentation until no hydrogen is generated.
[0022] Comparative Example 1: The difference from Example 1 is that in step S2, the pretreatment process is: sodium nitrite is added to the glass reactor containing the sludge sample, and the pH is adjusted to 5.5±0.1 with a 4 mol / L hydrochloric acid solution, and the free nitrite concentration in the glass reactor is controlled to be 0.73~1.29 mg / L.
[0023] Comparative Example 2: The difference from Example 1 is that, in step S2, the pretreatment process is: only citric acid is added to the glass reactor containing the sludge sample, and the amount of citric acid added is the same as the amount of citric acid added in Example 1.
[0024] Comparative Example 3: The difference from Example 1 is that in step S2, the pretreatment process is: using 4 mol / L hydrochloric acid solution to adjust the pH of the sludge sample to 5.5±0.1.
[0025] Comparative Example 4: The difference from Example 1 is that in step S2, no pretreatment is performed.
[0026] The comparison of hydrogen accumulation effect during anaerobic fermentation of sludge in Example 1 and Comparative Examples 1-4 is shown in Table 1. As can be seen from Table 1, the hydrogen production of sludge pretreated with free nitrite and citric acid in Example 1 is the highest, which is 1.1 times higher than the hydrogen production of Comparative Example 1 in which sludge is pretreated with free nitrite and hydrochloric acid. This shows that pretreatment of sludge with free nitrite and citric acid can enhance the inhibitory effect on hydrogen-consuming microorganisms in the anaerobic fermentation system of sludge, enhance the destructive effect on the extracellular polymers and cells of sludge microorganisms, and accelerate the release of intracellular substances in sludge, providing reaction substrates for fermentation hydrogen-producing microorganisms.
[0027] In addition, using citric acid instead of traditional inorganic acids (such as hydrochloric acid) for acid-base adjustment, firstly, reduces the production of inorganic salts and does not cause secondary pollution to the sludge; secondly, citric acid itself acts as a carbon source, providing more reaction substrates for fermentation and hydrogen-producing microorganisms; finally, the addition of citric acid improves the sludge C / N ratio, eliminates the nitrogen load brought by free nitrite, and helps the sludge fermentation to produce hydrogen.
[0028] Table 1 Hydrogen accumulation effect during anaerobic fermentation of sludge in Example 1 and Comparative Examples 1-4
[0029]
[0030] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention should also fall within the protection scope of the present invention.
Claims
1. A method for enhancing anaerobic fermentation of sludge to produce hydrogen, characterized in that: The following steps are involved: S1. After sieving the sludge, refrigerate and let it stand, and discard the supernatant to obtain a sludge sample; S2. After the sludge sample is restored to room temperature, it is placed in a glass reactor for pretreatment. Sodium nitrite is added to the glass reactor containing the sludge sample, and the pH is adjusted to 5.5±0.1 with citric acid. The concentration of free nitrite in the glass reactor is controlled to be 0.73-1.29 mg / L, and the pretreatment time is 4-5 h. S3, after the pretreatment is completed, nitrogen is charged into the glass reactor of step S2 to remove oxygen in the glass reactor; S4. After sealing the glass reactor, place it in an air bath constant temperature shaking incubator for anaerobic fermentation until no hydrogen is generated.
2. The method for enhancing anaerobic fermentation of sludge to produce hydrogen according to claim 1, characterized in that: In step S4, the temperature of the shaking table is 35±1°C and the rotation speed is 120 rpm.
3. The method for enhancing anaerobic fermentation of sludge to produce hydrogen according to claim 2, characterized in that: In step S3, nitrogen is charged into the glass reactor for 5 to 10 minutes.
4. The method for enhancing sludge anaerobic fermentation to produce hydrogen according to claim 3, characterized in that: In step S1, the refrigeration temperature is 4°C and the standing time is 12 to 24 hours.
5. The method for enhancing anaerobic fermentation of sludge to produce hydrogen according to claim 4, characterized in that: In step S2, the initial concentration of sodium nitrite in the glass reactor is 180 mg / L, and the cumulative dosage of citric acid is 215±10 mg.