A modified biochar and a preparation method and application thereof

Abstract

This invention relates to a modified biochar and its preparation method, comprising: (1) selecting biochar, preferably sludge-based biochar, acid treatment, and sieving; (2) mixing the biochar with a dopamine solution, reacting fully, and drying to obtain a first product; (3) immersing the first product in an AHLs solution, reacting, removing it, and drying to obtain modified biochar. The modified biochar provided by this invention has a suitable pore structure and AHLs signal molecule content, enabling the slow release of AHLs signal molecules, and is not easily degraded or lost. When used to prepare granular sludge, it has advantages such as short granulation time, stable particles, and good removal effect of carbon and nitrogen pollutants.

Description

Technical Field

[0001] This invention belongs to the field of water pollution control technology, specifically relating to a modified biochar, its preparation method, and its application. Background Technology

[0002] Anaerobic digestion can convert organic matter in wastewater into methane for recycling in an anaerobic environment through the synergistic effect of various functional microbial communities. However, it suffers from long reactor start-up times, slow sludge granulation rates, and the sludge structure is susceptible to substrate impact. During sludge formation, the added substrate provides conditions for microbial attachment and growth, which is beneficial for sludge formation.

[0003] Biochar has high porosity and a large specific surface area, exhibiting strong loading capacity, making it an ideal carrier for microbial immobilization. CN114014441A discloses a method for rapidly improving the activity and abundance of anaerobic ammonia oxidizing bacteria by adding redox activated biochar. The method involves adding redox activated biochar to low-abundance anaerobic ammonia oxidizing sludge, with the addition amount being 3–14 g / L. The redox activated biochar is selected as bamboo charcoal-based biochar prepared from bamboo, with a particle size of 20–40 micrometers. This invention can increase the denitrification activity and abundance of anaerobic ammonia oxidizing bacteria by adding redox activated biochar. However, the suitable carrier type and substrate vary for different microbial culture systems, and it lacks universal applicability; furthermore, conventional carriers have no significant impact on bacterial activity.

[0004] In recent years, technologies that enhance granular sludge formation through microbial quorum sensing have received widespread attention. Homoserine lactones (AHLs) are signaling molecules used by Gram-negative bacteria for communication and coordinating communal microbial behavior. The microbial communal behaviors regulated by AHLs include the degradation of specific organic matter, EPS secretion, and biofilm aggregation and formation. EPS secretion and biofilm aggregation and formation are closely related to sludge granulation. Due to their widespread presence in various microorganisms and their versatility, it is possible to utilize AHLs to regulate microbial communal behavior in wastewater biological treatment projects.

[0005] CN107352646A discloses an integrated device and method for promoting anaerobic sludge granulation, belonging to the field of organic wastewater treatment. The device includes an equalization tank, a reactor body, and an effluent tank, as well as an influent pump, an external circulation pump, a dosing pump, and a dosing device integrated inside the reactor body. It can effectively improve the contact efficiency between homoserine lactone (AHL) signaling molecules and anaerobic sludge, thereby increasing the granulation rate. Compared with existing technologies, this method for promoting anaerobic sludge granulation can shorten the granulation time, and the resulting granular sludge has good stability and is easy to operate.

[0006] CN107352647A discloses a method for improving the granulation efficiency of anaerobic sludge. Addressing the problems of long cultivation cycles, poor particle stability, and high cultivation costs in existing anaerobic granular sludge technologies, the method involves periodically adding an appropriate amount of organically synthesized homoserine lactone (AHL) signaling molecules to the bottom of the EGSB reactor used for anaerobic sludge granulation cultivation, mixing it with the anaerobic sludge. The addition cycle is equal to the hydraulic retention time, achieving high anaerobic sludge granulation efficiency, low cost, and significantly shortening the granulation time.

[0007] Although there is a very strong correlation between the concentration of quorum sensing signaling molecules (AHLs) and sludge granulation, current methods primarily involve the direct addition of exogenous signaling molecules. This method has the following drawbacks: the signaling molecules introduced into the system are easily degraded and lost, failing to achieve a long-term positive effect; and the cost of long-term addition of exogenous signaling molecules is high, limiting its widespread practical application. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention provides a modified biochar, its preparation method, and its applications. The modified biochar provided by this invention possesses a suitable pore structure and AHLs signaling molecule content, enabling the slow release of AHLs signaling molecules. It is also resistant to degradation and loss. When used to prepare granular sludge, it offers advantages such as short granulation time, stable particles, and excellent removal of carbon and nitrogen pollutants.

[0009] The first aspect of this invention provides a method for preparing modified biochar, comprising the following:

[0010] (1) Select biochar, preferably sludge-based biochar, and acid-treat and sieve it;

[0011] (2) The biochar was mixed with dopamine solution, and after the reaction was completed, it was dried to obtain the first product;

[0012] (3) The first product was immersed in an AHLs solution. After the reaction was completed, it was dried to obtain modified biochar.

[0013] Further, the biochar mentioned in step (1) can be biochar prepared from wood, straw, or agricultural waste, and can be obtained through self-production or commercial purchase. More preferably, the specific surface area of ​​the biochar is 10-900 m². 2 / g, average pore size 3-100nm, total pore volume 0.01-0.50cm³ 3 / g.

[0014] Further, the biochar in step (1) is preferably sludge-based biochar, that is, biochar prepared from the residual activated sludge of a wastewater treatment plant. More preferably, the sludge-based biochar is prepared by the following method: the residual sludge is washed, dried, ground into powder, and carbonized under an inert atmosphere to obtain biochar. The residual activated sludge is selected from the sludge of the secondary sedimentation tank of a wastewater treatment plant, washed to remove surface impurities, and dried to constant weight at 70-85℃. The inert atmosphere can be under inert gas or nitrogen conditions; the carbonization temperature is 600-900℃, the carbonization time is 1-3h, and the heating rate is 5-10℃ / min.

[0015] Further, the acid treatment in step (1) involves immersion in an inorganic acid for 4-8 hours, preferably at least one of hydrochloric acid, nitric acid, or sulfuric acid, with a concentration of 0.2-1.2 mol / L. After acid treatment, the sample is removed, washed until neutral, dried at 70-85°C, and passed through a 50-150 mesh sieve.

[0016] Further, the dopamine solution in step (2) is prepared by dissolving dopamine hydrochloride in a Tris solution, resulting in a dopamine concentration of 2.0-3.0 g / L, and adjusting the pH to 8.0-9.0. HCl or NaOH can be used to adjust the pH. The Tris (trihydroxyaminomethane) solution has a concentration of 1.0-2.0 g / L and can be prepared in-house or commercially available. More preferably, ethanol is added to the Tris solution at a volume ratio of 1:2-8 to the Tris solution.

[0017] Further, the mass-to-volume ratio of biochar to dopamine solution in step (2) is 1 g: 25-35 mL. The reaction is stirred at room temperature for 8-15 h.

[0018] Further, after the reaction in step (2) is completed, remove the product and dry it at 50-60℃ for 1-5 hours.

[0019] Further, the AHLs solution in step (3) is a mixture of AHLs signaling molecules and a solvent, wherein the concentration of AHLs signaling molecules in the solvent is 2.0-4.0 mg / L. The solvent is at least one of ethyl acetate, methanol, etc. AHL signaling molecules can be extracted from biological units or are commercially available products. Preferably, they are one or more of the homoserine lactones, and more preferably one or more of the following: butyryl homoserine lactone (C4-HSL), hexanoyl homoserine lactone (C6-HSL), octanoyl homoserine lactone (C8-HSL), decanoyl homoserine lactone (C10-HSL), dodecanoyl homoserine lactone (C12-HSL), tetradecanoyl homoserine lactone (C14-HSL), 3-oxohexanoyl homoserine lactone (3OC6-HSL), 3-oxooctanoyl homoserine lactone (3OC8-HSL), 3-oxodecanoyl homoserine lactone (3OC10-HSL), 3-oxododecanoyl homoserine lactone (3OC12-HSL), and 3-oxotetradecanoyl homoserine lactone (3OC14-HSL).

[0020] Further, in step (3), the ratio of the first product to the AHLs solution is 1g: 25-50mL, the soaking time is 2-4h, and the pH is 6-8.

[0021] Further, after the reaction in step (3) is completed, remove the product and dry it at 20-30℃ for 1-5 hours.

[0022] A second aspect of this invention provides a modified biochar prepared using the method described above. Based on the total mass of the biochar, the dopamine content is 4%-7%, and the AHLs content is 0.005%-0.02%.

[0023] A third aspect of this invention provides the application of the modified biochar provided by the present invention as a carrier in a granular sludge formation process. The granular sludge is preferably anaerobic granular sludge. The granular sludge formation process involves adding the modified biochar to an anaerobic reaction system, whereby the sludge is loaded onto the biochar and forms granules.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) The modified biochar provided by the present invention has a suitable pore structure and AHLs signaling molecule content. It promotes the adsorption of microorganisms on the surface of biochar and accelerates the sludge granulation process by stimulating the secretion of EPS by cells through AHLs signaling molecules. It has the advantages of short granulation time and good removal effect of carbon and nitrogen pollutants.

[0026] (2) The present invention first uses dopamine-modified biochar and then loads AHLs signaling molecules, which can achieve the slow release of AHLs signaling molecules, thereby avoiding the degradation and loss of AHLs signaling molecules and improving particle stability.

[0027] (3) The present invention performs acid treatment on biochar, which is beneficial for dopamine to more comprehensively modify biochar and load suitable AHLs signaling molecules, thereby improving the binding performance of the two. Detailed Implementation

[0028] The technical solution and its effects of the present invention will be described in detail below with reference to specific embodiments. These embodiments are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operating procedures; however, the scope of protection of the present invention is not limited to the following embodiments.

[0029] Unless otherwise specified, the experimental methods used in the following examples are conventional methods in the art. Unless otherwise specified, the experimental materials used in the following examples were purchased from conventional biochemical reagent stores.

[0030] Example 1

[0031] (1) Take the residual sludge from the secondary sedimentation tank of the sewage treatment plant, wash it with water three times to remove surface impurities, dry it at 80℃ to constant weight, grind it into powder, and carbonize it at 700℃ for 2 hours in a tube furnace under nitrogen conditions at a heating rate of 5℃ / min. After cooling to room temperature, soak it in 1.0mol / L HCl solution and stir for 6 hours. Wash it with deionized water until neutral, dry it at 80℃ and pass it through a 100-mesh sieve to obtain sludge-based biochar.

[0032] (2) Dopamine hydrochloride was dissolved in a Tris-ethanol mixture with a Tris concentration of 1.0 g / L and a Tris to ethanol volume ratio of 5:1. The dopamine concentration was 2.0 g / L, and the pH was adjusted to 8.5 using 0.1 M NaOH. Biochar powder was added to the dopamine solution at a ratio of 1 g: 28 mL, and the mixture was stirred at room temperature for 12 h. After the reaction was complete, the mixture was removed and dried at 50 °C for 2 h to obtain the first product.

[0033] (3) 3OC6-HSL was dissolved in ethyl acetate, and the concentration of AHLs signaling molecules was 3.2 mg / L. The ratio of the first product to the AHLs solution was 1 g: 37.5 mL, the impregnation time was 3 h, and the pH was 7.0. After the reaction was completed, the product was removed and dried at 25 °C for 2 h to obtain modified biochar.

[0034] Example 2

[0035] (1) The remaining sludge was washed with water three times to remove surface impurities, dried at 80°C to constant weight, ground into powder, and carbonized at 700°C for 2 hours in a tube furnace under nitrogen conditions at a heating rate of 5°C / min. After cooling to room temperature, it was added to a 1.0 mol / L HCl solution and stirred for 4 hours. The mixture was filtered and washed with deionized water until the filtrate was neutral. It was then dried at 80°C and passed through an 80-mesh sieve to obtain sludge-based biochar.

[0036] (2) Dopamine hydrochloride was dissolved in a Tris-ethanol mixture with a Tris concentration of 1.0 g / L and a Tris to ethanol volume ratio of 4:1. The dopamine concentration was 3.0 g / L, and the pH was adjusted to 8.5 using 0.1 M NaOH. Biochar powder was added to 30 mL of the dopamine solution, and the mixture was magnetically stirred for 12 h at room temperature. After the reaction was complete, the mixture was removed and dried at 50 °C for 2 h to obtain the first product.

[0037] (3) Commercially available 3OC6-HSL was dissolved in ethyl acetate, and the concentration of AHLs signaling molecules in the solvent was 4.0 mg / L. The ratio of the first product to the AHLs solution was 1 g: 25 mL, the impregnation time was 3 h, and the pH was 7.0. After the reaction was completed, the product was removed and dried at 25 °C for 2 h to obtain modified biochar.

[0038] Example 3

[0039] (1) The remaining sludge was washed with water three times to remove surface impurities, dried at 80°C to constant weight, ground into powder, and carbonized at 700°C for 2 hours in a tube furnace under nitrogen conditions at a heating rate of 5°C / min. After cooling to room temperature, it was added to a 1.0 mol / L HCl solution and stirred for 8 hours. The mixture was filtered and washed with deionized water until the filtrate was neutral. It was then dried at 80°C and passed through a 120-mesh sieve to obtain sludge-based biochar.

[0040] (2) Dopamine hydrochloride was dissolved in a Tris-ethanol mixture with a Tris concentration of 1.0 g / L and a Tris to ethanol volume ratio of 6:1. The dopamine concentration was 2.4 g / L, and the pH was adjusted to 8.5 using 0.1 M NaOH. Biochar powder was added to 35 mL of the dopamine solution and stirred at room temperature for 12 h. After the reaction was complete, the solution was removed and dried at 50 °C for 2 h to obtain the first product.

[0041] (3) Commercially available 3OC6-HSL was dissolved in ethyl acetate, and the concentration of AHLs signaling molecules in the solvent was 2 mg / L. The ratio of the first product to the AHLs solution was 1 g: 50 mL, the impregnation time was 3 h, and the pH was 7.0. After the reaction was completed, the product was removed and dried at 25 °C for 2 h to obtain modified biochar.

[0042] Example 4

[0043] Same as Example 1, except that straw-based biochar was used. The final product was modified biochar.

[0044] Example 5

[0045] Similar to Example 1, except that the AHLs signaling molecules were mixed with a solvent, which was methanol. The resulting modified biochar was obtained.

[0046] Example 6

[0047] Same as Example 1, except that in step (2) of preparing the dopamine solution, a Tris solution without ethanol was used as the solvent. Modified biochar was finally obtained.

[0048] Comparative Example 1

[0049] Same as Example 1, except that: step (1) acid treatment process is omitted, and the biochar is directly mixed with dopamine solution after sieving to finally obtain modified biochar.

[0050] Comparative Example 2

[0051] Same as Example 1, except that step (2) is omitted, and the biochar after sieving in step (1) is used instead of the first product in step (3) to be impregnated in AHLs solution to finally obtain modified biochar.

[0052] Test case

[0053] Several anaerobic reactors with an effective volume of 5L were prepared in the laboratory. After inoculating 2.5L of anaerobic sludge, the MLSS in the reactor was 12g / L. Then, the modified biochar obtained in Examples 1-6 and Comparative Examples 1-2 was added to the anaerobic reactor at a rate of 20g per reactor for the cultivation of granular sludge. The cultivation conditions were: temperature 30-35℃, pH 7.5-8.0, hydraulic retention time 24h, and the influent was self-made simulated wastewater with a COD concentration of approximately 3000mg / L and a TN concentration of approximately 150mg / L. The cultivation of granular sludge was considered complete when the proportion of granular sludge larger than 1.0mm in the reactor reached more than 30%. The cultivated granular sludge was used for wastewater treatment in a certain enterprise with a COD concentration of 3200mg / L, a TN concentration of 156mg / L, and a hydraulic retention time of 24h. Under these conditions, the experiment was run continuously for 60 days, and the experimental results are shown in Table 1.

[0054] Table 1. Test results of the examples and comparative examples

[0055]

[0056]

[0057] As shown in Table 1, the modified biochar obtained in Examples 1-6 resulted in a shorter granular sludge cultivation time and relatively better carbon and nitrogen removal performance during long-term operation. In contrast, the modified biochar obtained in Comparative Examples 1-2 resulted in a longer granular sludge cultivation time and poorer treatment performance.

Claims

1. A method for preparing modified biochar, characterized in that... Includes the following: (1) Select biochar, preferably sludge-based biochar, and acid-treat and sieve it; (2) Mix biochar with dopamine solution, and after the reaction is complete, dry to obtain the first product; (3) The first product was immersed in an AHLs solution, and after the reaction was completed, it was dried to obtain modified biochar.

2. The method according to claim 1, characterized in that: The biochar mentioned in step (1) is prepared from wood, straw, or agricultural waste; preferably, the specific surface area of ​​the biochar is 10-900 m². 2 / g, average pore size 3-100nm, total pore volume 0.01-0.50cm³ 3 / g.

3. The method according to claim 1, characterized in that: Step (1) uses sludge-based biochar, which is biochar prepared from residual activated sludge. The preparation method is as follows: after washing and drying the residual sludge, it is ground into powder and carbonized under an inert atmosphere to obtain sludge-based biochar.

4. The method according to claim 3, characterized in that: The remaining activated sludge comes from the secondary sedimentation tank sludge of the wastewater treatment plant. It is washed to remove surface impurities and dried at 70-85℃ to constant weight.

5. The method according to claim 3, characterized in that: An inert atmosphere refers to an environment under inert gas or nitrogen conditions; the carbonization temperature is 600-900℃, the carbonization time is 1-3h, and the heating rate is 5-10℃ / min.

6. The method according to claim 1, characterized in that: The acid treatment involves immersion in an inorganic acid for 4-8 hours, preferably at least one of hydrochloric acid, nitric acid, and sulfuric acid, with a concentration of 0.2-1.2 mol / L.

7. The method according to claim 1, characterized in that: After acid treatment, remove and wash until neutral, dry at 70-85℃, and pass through a 50-150 mesh sieve.

8. The method according to claim 1, characterized in that: The dopamine solution in step (2) is made by dissolving dopamine hydrochloride in Tris solution, with a dopamine concentration of 2.0-3.0 g / L and pH adjusted to 8.0-9.

0.

9. The method according to claim 8, characterized in that: Add ethanol to the Tris solution at a volume ratio of 1:2-8.

10. The method according to claim 1 or 8, characterized in that: In step (2), the mass-to-volume ratio of biochar to dopamine solution is 1g:25-35mL, and the reaction is carried out by stirring at room temperature for 8-15 hours.

11. The method according to claim 1, characterized in that: After the reaction in step (2) is completed, remove the product and dry it at 50-60℃ for 1-5 hours.

12. The method according to claim 1, characterized in that: Step (3) The AHLs solution is made by mixing AHLs signaling molecules with a solvent, wherein the concentration of AHLs signaling molecules in the solvent is 2.0-4.0 mg / L; the solvent is at least one of ethyl acetate and methanol.

13. The method according to claim 1 or 12, characterized in that: AHLs are selected from one or more homoserine lactones, preferably one or more of butyryl homoserine lactone, hexanoyl homoserine lactone, octanoyl homoserine lactone, decanoyl homoserine lactone, dodecanoyl homoserine lactone, tetradecanoyl homoserine lactone, 3-oxohexanoyl homoserine lactone, 3-oxooctanoyl homoserine lactone, 3-oxodecanoyl homoserine lactone, 3-oxododecanoyl homoserine lactone, and 3-oxotetradecanoyl homoserine lactone.

14. The method according to claim 1, 12 or 13, characterized in that: Step (3) The ratio of the first product to the AHLs solution is 1g:25-50mL, the soaking time is 2-4h, and the pH is 6-8.

15. The method according to claim 1, characterized in that: After the reaction in step (3) is completed, remove the product and dry it at 20-30℃ for 1-5 hours.

16. A modified biochar, characterized in that it is prepared by the method described in any one of claims 1-15, and has a dopamine content of 4%-7% and an AHLs content of 0.005%-0.02% by weight of total biochar.

17. The application of biochar prepared by the method according to any one of claims 1-15 or the biochar according to claim 15, characterized in that... Used as a carrier in the granular sludge formation process.

18. The application according to claim 17, characterized in that: The granular sludge is preferably anaerobic granular sludge.

19. The application according to claim 17, characterized in that: The process of forming granular sludge involves adding modified biochar to an anaerobic reaction system, where activated sludge is loaded onto the biochar and forms granules.

Images