A method for promoting anaerobic digestion of sludge by coupling treatment of oxygen and corn straw digestate biochar
Through the coupling treatment method of oxygen and corn straw sludge biochar, the problems of slow hydrolysis rate and low methane production rate during anaerobic sludge digestion were solved, efficient sludge anaerobic digestion and energy recovery were achieved, the operation process was simplified and costs were reduced.
Patent Information
- Application Number
- CN202310025148.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2023-01-09
- Publication Date
- 2025-09-16
- Estimated Expiration
- 2043-01-09
AI Technical Summary
In the existing technology, the anaerobic digestion process of sludge has problems such as slow hydrolysis rate, long digestion cycle, low methane production rate and small methane production amount. In addition, oxygen has a toxic effect on the anaerobic digestion system, resulting in acidification and low methane production rate.
A coupled treatment method of oxygen and corn straw digestate biochar was adopted. By adding residual sludge, inoculum and corn straw digestate biochar into the fermentation tank, oxygen was introduced and the anaerobic digestion conditions were controlled to promote the hydrolysis, acidification and methanogenesis of the sludge, and utilize the electron exchange capacity of biochar to accelerate the conversion of VFAs to methane.
It significantly improves the cumulative methane production, maximum methane production rate and potential of the anaerobic digestion process, simplifies the operation and reduces costs without causing secondary environmental pollution.
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Figure CN116002939B_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of solid waste resource treatment, and specifically relates to a method for promoting the anaerobic digestion process of sludge by coupling treatment of oxygen and corn straw sludge biochar. Background Art
[0002] With my country's rapid economic development and rising urbanization, the construction of urban sewage treatment plants has accelerated. According to statistics, in 2018, there were 3,802 sewage treatment plants nationwide, with a daily treatment capacity of 161 million cubic meters. Annual production of excess sludge, a byproduct of sewage treatment, has increased from 40 million tons in 2017 to 60 million tons in 2020. Adopting simple, effective, and cost-effective methods for the treatment and disposal of excess sludge is crucial for promoting the development of sewage treatment in my country and protecting public environmental safety.
[0003] Anaerobic digestion technology is considered an ideal treatment method for stabilizing, reducing, and detoxifying excess sludge due to its advantages, including simple operating conditions, low cost, pathogen inactivation, and biogas production. However, due to the complex composition of excess sludge, anaerobic digestion suffers from shortcomings such as low hydrolysis rates, long digestion cycles, low methane production rates, and low methane production. These shortcomings severely restrict the efficiency of anaerobic digestion of excess sludge and its energy recovery.
[0004] Introducing a small amount of oxygen in situ into an anaerobic system stimulates the growth of facultative bacteria, increasing the activity of proteases and cellulases in the anaerobic digestion system, accelerating the hydrolysis and acidification of excess sludge and increasing methane production. However, oxygen is toxic to anaerobic bacteria, especially methanogenic archaea. Furthermore, the increased concentration of volatile fatty acids (VFAs) promoted by oxygen further inhibits the growth of methanogenic archaea, disrupting the balance between syntrophic bacteria and methanogens, causing acidification in the anaerobic reactor and even leading to reactor failure.
[0005] Adding conductive materials (such as biochar) to anaerobic digestion systems can quickly transfer electrons produced by VFA-oxidizing bacteria to methanogens, accelerating the oxidative degradation of VFAs while also producing methane through the electron-reduced CO2 pathway, thereby increasing the rate of methane production. However, some studies have found that conductive materials have no significant effect on increasing the cumulative methane production from anaerobic digestion of excess sludge.
[0006] Therefore, it is necessary to develop an anaerobic sludge treatment technology to accelerate the generation of VFAs while promoting the conversion of VFAs to methane, ultimately achieving the goal of increasing the cumulative methane production. Summary of the Invention
[0007] [Technical Issues]
[0008] There is no relatively economical technology in the existing technology that can simultaneously achieve the technical effects of accelerating the decomposition of sludge to produce VFAs and promoting the conversion of VFAs to methane. The acidification phenomenon and low methane production rate in the sludge digestion process are still the pain points and difficulties in anaerobic sludge treatment.
[0009] [Technical solution]
[0010] In response to the shortcomings and bottlenecks of existing treatment technologies, the purpose of the present invention is to develop a method for promoting the anaerobic digestion process of sludge by coupling oxygen and corn straw sludge biochar treatment. By coordinating oxygen treatment with biochar treatment, the anaerobic digestion hydrolysis, acidification, hydrogen and acetic acid production, and methane production processes of residual sludge are promoted, thereby improving the cumulative methane production and energy recovery efficiency.
[0011] The technical solution of the present invention is achieved by the following steps:
[0012] The first object of the present invention is to provide a method for promoting the anaerobic digestion process of sludge by coupling oxygen and corn straw digestate biochar. The method comprises adding residual sludge, inoculum and corn straw digestate biochar into a fermentation tank, then adding water to adjust the operating volume, sealing the fermentation tank, introducing oxygen, carrying out anaerobic digestion reaction of sludge, and regularly measuring the biogas volume and methane content.
[0013] In one embodiment, the excess sludge comes from the sludge discharged from the plate and frame filter press of a municipal sewage treatment plant.
[0014] In one embodiment, the inoculum is sludge discharged from a long-term anaerobic digestion reactor, which contains abundant syntrophic microorganisms such as Cloacimonadia and Methanobacterium (see the literature "The effects of micro-aeration on semi-continued anaerobic digestion of corn straw with increasing organic loading rates").
[0015] In one embodiment, the specific preparation process of the corn straw sludge biochar is as follows: the corn straw sludge is dried at 105°C and then mechanically crushed, sieved, and then laid flat in a tubular furnace. The carbonization temperature is controlled to 550-600°C, the heating rate is controlled to 20°C / minute, the carbonization time is 0.5-0.9h, and nitrogen is passed through the tubular furnace for 10 minutes before heating to remove the air, and nitrogen is continuously passed through for protection during the carbonization and cooling process.
[0016] In one embodiment, the maximum particle size of the corn straw biogas residue after crushing and screening is <0.15 mm.
[0017] In one embodiment, the contents of hemicellulose, cellulose, and lignin in the corn straw biogas residue are 9.5%±1.4%, 21.6%±1.6%, and 33.3%±3.7%, respectively.
[0018] In one embodiment, the surface of the corn straw digestate biochar has C—OH and C═O oxygen-containing functional groups.
[0019] In one embodiment, the surface O / C of the corn straw digestate biochar is 0.3, and the proportions of C-OH and C=O oxygen-containing functional groups are 21.1% and 18.7%, respectively.
[0020] In one embodiment, the electron exchange capacity of the corn straw digestate biochar is ≥41.5 μmole - / g.
[0021] In one embodiment, the mass ratio of the excess sludge to the inoculum is 2 to 5:1.
[0022] In one embodiment, the mass ratio of the corn straw biogas residue biochar to the residual sludge is 1-2:15-20.
[0023] In one embodiment, the oxygen feed rate is 150-600 mL / L 反应器 , preferably 600mL / L 反应器 .
[0024] In one embodiment, nitrogen is required to be passed through the fermentation tank to remove air from the tank before sealing the fermentation tank.
[0025] In one embodiment, the anaerobic digestion reaction is carried out under the following conditions: the operating temperature is controlled at 37±1° C., the shaking speed is 200 rpm, and the anaerobic digestion cycle is 30 days.
[0026] In one embodiment, the running volume is 200-300 mL.
[0027] The second object of the present invention is to provide an application of the above-mentioned method in the field of solid waste treatment.
[0028] A third object of the present invention is to provide a method for increasing methane production in sludge, the method comprising adding excess sludge, inoculum, and corn straw digestate biochar into a fermentation tank, then adding water to adjust the operating volume, sealing the fermentation tank, introducing oxygen, performing anaerobic digestion of the sludge, and regularly measuring the biogas volume and methane content.
[0029] [Beneficial Effects]
[0030] 1. The oxygen source used by the present invention to stimulate the growth of facultative bacteria is rich, the operation is simple, and the dosage is small (only 600mL / L is needed). 反应器 ), low cost and will not cause secondary pollution to the environment.
[0031] 2. The present invention uses corn straw after anaerobic digestion to prepare biochar, which has abundant surface oxygen-containing functional groups and an electron exchange capacity of ≥41.5μmole - / g biochar, which can accelerate the direct electron transfer rate between symbiotic microorganisms.
[0032] 3. The advantages of the present invention's coupled oxygen treatment and biochar treatment technology are that, compared to the control, oxygen-coupled biochar treatment can accelerate the maximum methane production rate by 21.1%, increase the maximum methane production potential by 11.9%, and increase the cumulative methane production during anaerobic digestion by 13.3%. Oxygen-coupled biochar treatment significantly increases cumulative methane production and enhances the anaerobic digestion process of excess sludge. BRIEF DESCRIPTION OF THE DRAWINGS
[0033] Figure 1 This is a diagram showing the types of oxygen-containing functional groups on the surface of corn straw digestate biochar characterized by Fourier transform infrared spectroscopy in the present invention;
[0034] Figure 2 This is a composition ratio diagram of oxygen-containing functional groups on the surface of corn straw digestate biochar characterized by XPS in the present invention;
[0035] Figure 3 This is a data diagram of the electron exchange capacity of corn straw digestate biochar characterized by cyclic voltammetry in the present invention;
[0036] Figure 4 This is a graph showing the cumulative methane production during the anaerobic digestion process of the control group, oxygen group, biochar group, and oxygen-coupled biochar group. DETAILED DESCRIPTION
[0037] The following is a detailed, specific and complete description of the technical solutions for implementing the present invention.
[0038] 1. Measuring biogas volume by drainage method
[0039] The biogas in the sealed fermentation tank enters a sealed glass bottle containing saturated sodium bicarbonate solution through an exhaust pipe. The volume of the discharged saturated sodium bicarbonate solution is collected and measured by a measuring cylinder, which is the biogas volume.
[0040] 2. Gas chromatography to measure methane content
[0041] The components in biogas were determined using an SP-6890 gas chromatograph and a TCD conductivity detector. The temperatures of the inlet, chromatographic column, and detector were set to 50°C, 100°C, and 100°C, respectively. The carrier gas was high-purity argon, and the biogas inlet volume was 0.4 mL.
[0042] The modified Gompetz equation was used to fit the cumulative methane production data obtained from the experiment to analyze the maximum methane production potential and maximum methane production rate of the anaerobic digestion process.
[0043] 3. Preparation of biochar according to the present invention
[0044] The corn straw sludge is dried at 105℃ and then mechanically crushed. The maximum particle size is controlled by sieving to <0.15mm, and then it is spread flat in a tubular furnace. The carbonization temperature is controlled at 550-600℃, the heating rate is controlled at 20℃ / min, and the carbonization time is 0.5-0.9h. Nitrogen is passed through the tubular furnace for 10 minutes before heating to remove the air, and nitrogen is continuously passed through for protection during the carbonization and cooling process.
[0045] The contents of hemicellulose, cellulose, and lignin in corn straw biochar were 9.5% ± 1.4%, 21.6% ± 1.6%, and 33.3% ± 3.7%, respectively. The surface of corn straw biochar contained C-OH and C=O oxygen-containing functional groups, with a surface O / C ratio of 0.3. The ratios of C-OH and C=O oxygen-containing functional groups were 21.1% and 18.7%, respectively. The electron exchange capacity of corn straw biochar was ≥ 41.5 μmole - / g biochar.
[0046] 4. The substrate used in the present invention is residual sludge, which comes from the mud discharged from the plate and frame filter press of the municipal sewage treatment plant; oxygen is purchased from Wuxi Xinxiyi Gas Equipment Co., Ltd. from a gas company.
[0047] The inoculum was obtained from the sludge discharged from a long-term anaerobic digestion reactor in the laboratory, which contains abundant mutualistic microorganisms such as Cloacimonadia and Methanobacterium (see the literature The effects of micro-aeration on semi-continued anaerobic digestion of corn straw with increasing organic loading rates).
[0048] Example 1
[0049] A method for promoting anaerobic digestion of sludge by coupling treatment of oxygen and corn straw digestate biochar, specifically comprising the following steps:
[0050] 18 g TS (total solid content) residual sludge, 6 g TS inoculum and 1.6 g corn straw digestate biochar were added to a 300 mL fermentation bottle, and the actual operating volume was adjusted to 200 mL by adding tap water. After exposure to nitrogen for 5 minutes, it was sealed with a rubber stopper and an aluminum cap. 120 mL of oxygen was injected at one time. The operating temperature was controlled at 37 ± 1 °C, the shaking speed was 200 rpm, and the anaerobic digestion cycle was 30 days. The biogas volume was measured regularly by the drainage method and the methane content was measured by gas chromatography every day.
[0051] In the above scheme, 120mL of oxygen (600mL / L) was added at one time. 反应器 ) and 1.6g(8g / L 反应器 The anaerobic digestion system containing biochar was called oxygen + biochar group, with a final cumulative methane production of 92.6±1.2mL / g VS, a maximum methane production rate of 6.7±0.6mL / g VS / d, and a maximum methane production potential of 86.8±2.7mL / g VS.
[0052] Example 2 Optimization of oxygen usage
[0053] The amount of oxygen used in Example 1 was adjusted to 30 mL oxygen (150 mL / L 反应器 )、60mL oxygen (300mL / L 反应器 ) and 90mL oxygen (450mL / L 反应器 ); other conditions remain the same as in Example 1;
[0054] Results: When the oxygen volume is 150mL / L 反应器 When the oxygen content was 300mL / L, the final cumulative methane production was 87.2±0.3mL / g VS, the maximum methane production rate was 6.2±0.5mL / g VS / d, and the maximum methane production potential was 82.4±2.4mL / g VS. 反应器 When the oxygen content was 450mL / L, the final cumulative methane production was 84.5±1.5mL / g VS, the maximum methane production rate was 6.5±0.6mL / g VS / d, and the maximum methane production potential was 78.7±2.4mL / g VS. 反应器 When , the final cumulative methane production was 90.2±0.7mL / g VS, the maximum methane production rate was 6.6±0.6mL / g VS / d, and the maximum methane production potential was 84.8±2.7mL / g VS.
[0055] Comparative Example 1
[0056] 18 g of TS residual sludge and 6 g of TS inoculum were added to a 300 mL fermentation bottle, and the actual operating volume was adjusted to 200 mL by adding tap water. After exposure to nitrogen for 5 minutes, the bottle was sealed with a rubber stopper and an aluminum cap. The operating temperature was controlled at 37 ± 1 °C, the shaking speed was 200 rpm, and the anaerobic digestion cycle was 30 days. The biogas volume was measured regularly by the drainage method and the methane content was measured by gas chromatography every day.
[0057] In the above scheme, the anaerobic digestion system without adding oxygen and biochar was called the control group. The final cumulative methane production was 81.7±1.8mL / g VS, the maximum methane production rate was 5.6±0.5mL / g VS / d, and the maximum methane production potential was 77.6±2.1mL / gVS.
[0058] Comparative Example 2
[0059] 18 g TS residual sludge, 6 g TS inoculum and 1.6 g corn straw digestate biochar were added to a 300 mL fermentation bottle, and the actual operating volume was adjusted to 200 mL by adding tap water. After exposure to nitrogen for 5 minutes, it was sealed with a rubber stopper and an aluminum cap. The operating temperature was controlled at 37 ± 1 °C, the shaking speed was 200 rpm, and the anaerobic digestion cycle was 30 days. The biogas volume was measured regularly by the drainage method and the methane content was measured by gas chromatography every day.
[0060] In the above scheme, the anaerobic digestion system with 1.6 g of biochar added was called the biochar group. The final cumulative methane production was 85.9 ± 0.6 mL / g VS, the maximum methane production rate was 5.8 ± 0.5 mL / g VS / d, and the maximum methane production potential was 81.5 ± 2.4 mL / g VS.
[0061] Comparative Example 3
[0062] 18 g of TS excess sludge and 6 g of TS inoculum were added to a 300 mL fermentation bottle, and the actual operating volume was adjusted to 200 mL by adding tap water. After exposure to nitrogen for 5 minutes, it was sealed with a rubber stopper and an aluminum cap. 120 mL of oxygen was injected at one time. The operating temperature was controlled at 37 ± 1 °C, the shaking speed was 200 rpm, and the anaerobic digestion cycle was 30 days. The biogas volume was measured regularly by the drainage method and the methane content was measured by gas chromatography every day.
[0063] In the above scheme, the anaerobic digestion system with a one-time addition of 120 mL of oxygen was called the oxygen group. The final cumulative methane production was 84.1 ± 2.7 mL / g VS, the maximum methane production rate was 5.9 ± 0.5 mL / g VS / d, and the maximum methane production potential was 79.3 ± 2.5 mL / gVS.
[0064] Result Analysis
[0065] Compared with the control group, the cumulative methane production, maximum methane production rate and maximum methane production potential of comparative example 2 (biochar group) increased by 5.1%, 5.1% and 4.5% respectively. This may be because although the biochar surface contains abundant C-OH and C=O oxygen-containing functional groups ( Figure 1 and Figure 2 ), which can increase the electron transfer rate of the anaerobic digestion system ( Figure 3 , biochar electron exchange capacity ≥ 41.5 μmole - / g biochar), accelerating the conversion of volatile fatty acids (VFAs) to methane. However, the composition of residual sludge is relatively complex, and the anaerobic hydrolysis and acidification rates are relatively slow, which cannot provide sufficient intermediate VFAs for the methanogenesis process. This limits the function of biochar as a direct interspecies electron carrier to accelerate the methanogenesis process. Therefore, biochar treatment alone has no obvious effect on the performance of the anaerobic digestion system.
[0066] Compared with the control group, the cumulative methane production, maximum methane production rate, and maximum methane production potential of Comparative Example 3 (oxygen group) increased by 3.0%, 2.2%, and 5.3%, respectively. This may be because, while oxygen can stimulate the growth of facultative bacteria, promote the secretion of proteases and cellulases, accelerate the acidification and hydrolysis of excess sludge, and increase the content of intermediate VFAs, the increased VFA content has an inhibitory or even toxic effect on methanogenic archaea. Therefore, oxygen treatment alone has a limited promoting effect on the anaerobic digestion system.
[0067] Compared with the control group (Table 1), the cumulative methane production, maximum methane production rate and maximum methane production potential of Example 1 (oxygen + biochar group) increased by 13.3%, 11.9% and 21.1%, respectively. The increase in oxygen dosage is beneficial to enhancing the performance of the anaerobic digestion system by coupling oxygen with biochar treatment. The optimal oxygen dosage is 600 mL / L. 反应器 (Table 2) This may be because the coupled oxygen and biochar treatment not only uses oxygen to stimulate the growth of facultative bacteria, accelerates the hydrolysis and acid production process of anaerobic digestion of excess sludge, and provides more intermediate VFAs for the methanogenesis process, but also uses the abundant C-OH and C=O oxygen-containing functional groups on the surface of biochar as electron carriers to accelerate the electron exchange rate between VFA-oxidizing bacteria and methanogens, promote the oxidative degradation of VFAs, significantly increase the maximum methanogenesis rate and maximum methanogenesis potential, and ultimately significantly increase the cumulative methane production of excess sludge anaerobic digestion.
[0068] Table 1 shows the data changes of Example 1 and Comparative Examples 2 and 3 compared with Comparative Example 1
[0069]
[0070] Table 2 Data changes between Example 1 and Example 2
[0071]
[0072] The above only introduces the technical solution of the present invention with reference to preferred embodiments. However, those skilled in the art should be able to make changes in the specific implementation methods and application scope based on the ideas of the embodiments of the present invention. Therefore, in summary, the content of this specification should not be understood as limiting the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of the claims of the present invention.
Claims
1. A method for promoting anaerobic digestion of sludge by coupling oxygen and corn straw digestate biochar, characterized in that: The method comprises adding excess sludge, inoculum and corn straw digestate biochar into a fermentation tank, then adding water to adjust the operating volume, sealing the fermentation tank, introducing oxygen to perform anaerobic digestion of the sludge, and regularly measuring the biogas volume and methane content; The oxygen flow rate is 600 mL / L 反应器； The mass ratio of the excess sludge to the inoculum is 2-5:1; The mass ratio of the corn straw biochar to the excess sludge is 1-2:15-20; The preparation process of corn straw biochar is as follows: the corn straw biochar is dried, mechanically crushed, sieved, and then laid flat in a tube furnace, and the carbonization temperature is controlled at 550-600 o C, the heating rate is controlled at 15~20 o C / min, the carbonization time is 0.5-0.9 h, nitrogen is passed through the tube furnace to remove the air before heating, and nitrogen is continuously passed through the carbonization and cooling process for protection.
2. The method according to claim 1, characterized in that The surface O / C of the corn straw biochar is 0.3, and the proportions of C-OH and C=O oxygen-containing functional groups are 21.1% and 18.7%, respectively.
3. The method according to claim 1, characterized in that The conditions of the anaerobic digestion reaction are as follows: the operating temperature is controlled at 37±1° C., the shaking speed is 200 rpm, and the anaerobic digestion cycle is 30 days.
4. The method according to claim 1, wherein The surface of the corn straw digestate biochar has C-OH and C=O oxygen-containing functional groups.
5. Use of the method according to any one of claims 1 to 4 in the field of solid waste treatment.
Citation Information
Patent Citations
Method for efficiently preparing magnetic biochar from straw and application
CN112938929A