Preparation method and application of sludge-based magnetic activated carbon material

Abstract

The invention discloses a preparation method and application of a sludge-based magnetic activated carbon material, and belongs to the field of activated carbon preparation.The method comprises the steps that pretreated sludge is mixed with a 3mol / L ZnCl2 activating agent solution under the conditions that the temperature is 30 DEG C and the solid-to-liquid ratio is 1: 2.5, dipping is conducted for 24 hours under the room temperature condition, drying is conducted, then carbonization is conducted, and the activated carbon material is obtained; preparing to obtain a sludge-based activated carbon base material; and adding the sludge-based activated carbon base material into a compound mixed solution obtained by compounding a FeCl2 / FeCl3 salt solution and a NH3.H2O solution, reacting, and drying to constant weight to obtain the sludge-based magnetic activated carbon. According to the invention, the degradation performance of the substrate in the anaerobic digestion process can be obviously enhanced.

Description

Technical Field

[0001] The present invention relates to the field of activated carbon preparation, and in particular to a preparation method of a sludge-based magnetic activated carbon material and application thereof. Background Art

[0002] There is an urgent need to reduce the total amount of biowaste. The rational, efficient, and economical treatment and disposal of excess sludge, which has a high moisture content, large production volume, and complex composition, has become a critical issue urgently needed in the fields of ecological protection and pollution control. Anaerobic digestion, as an effective and environmentally friendly energy production technology, offers the advantages of low energy consumption, low operating costs, high organic loading, and high biogas production. It not only harmlessly reduces solid organic waste, such as excess sludge, generated by municipal wastewater treatment plants, but also recovers methane, contributing to global carbon cycling and energy utilization.

[0003] Anaerobic digestion involves the decomposition of organic matter into stable substances such as organic acids and methane under anaerobic conditions using anaerobic and facultative microorganisms through three stages: hydrolysis and acidification, hydrogen and acetogenesis, and methanogenesis. This process reduces sludge volume and enables resource recycling. Briefly, in the initial acidogenesis stage, complex organic matter is broken down into simple organic matter, which is then further decomposed into volatile fatty acids and alcohols. These intermediates are then converted into acetic acid and hydrogen by syntrophic microorganisms during acetoacetogenesis. Finally, methanogens convert acetic acid and hydrogen into methane. Research has shown that CO2-mediated interspecies electron transfer, using hydrogen / formate as a diffusible electron carrier to transfer electrons from fatty acids or alcohols, has long been considered the primary pathway for methane production. However, only a low H2 partial pressure regulated by hydrogenotrophic methanogens provides thermodynamically feasible conditions for methane production by hydrolytic and fermentative bacteria. Furthermore, interspecies electron transfer of hydrogen and formate is significantly limited by low diffusion efficiency and strict intercellular distance requirements, severely limiting the rate of methane production during anaerobic digestion.

[0004] As an excellent redox medium, activated carbon can provide a large reaction surface area for the growth of microorganisms and the retention of biomass in anaerobic digestion reactors, facilitating greater electron transfer between electroactive co-trophic microorganisms. In addition, it has excellent electrical conductivity, biocompatibility, and catalytically active sites, which can provide better electron exchange interactions. It has been used in batch and continuous reactors with a variety of substrates such as ethanol, propanol, acetate, propionate, and activated sludge. Currently, the biomass materials commonly used to prepare activated carbon include plant-derived biomass, animal-derived biomass, and sludge biomass. The use of sludge biomass to prepare activated carbon materials can not only solve the problem of sludge treatment and disposal and promote the recycling of resources, but also improve the efficiency of anaerobic digestion of sludge, which is an important direction for achieving sustainable development of sludge treatment and disposal. Summary of the Invention

[0005] One of the purposes of the present invention is to provide a method for preparing sludge-based magnetic activated carbon materials to solve the problem of low degradation performance of substrates in anaerobic digestion processes in the prior art.

[0006] The present invention is achieved through the following technical solution. A method for preparing a sludge-based magnetic activated carbon material comprises the following steps: S100, mixing the pretreated sludge with a 3 mol / L ZnCl2 activator solution at 30°C and a solid-to-liquid ratio of 1:2.5, impregnating the sludge at room temperature for 24 hours, drying the mixture, and then carbonizing the mixture to obtain a sludge-based activated carbon substrate; S200, adding the sludge-based activated carbon substrate to a composite mixed solution obtained by compounding an FeCl2 / FeCl3 salt solution and an NH3·H2O solution, and drying the mixture to a constant weight after the reaction to obtain the sludge-based magnetic activated carbon.

[0007] Furthermore, the sludge comes from a sewage treatment plant, and the pretreatment includes: naturally drying the sludge to a moisture content of 10%.

[0008] Furthermore, the drying step comprises drying the impregnated sludge to a constant weight at 105° C.; the carbonization step comprises crushing the sludge dried to a constant weight and then placing it in a tubular resistance furnace at 600° C. for carbonization for 60 minutes. After carbonization, the sludge is soaked in a 3 mol / L HCl solution for 30 minutes, then rinsed with deionized water until neutral, and finally dried at 45° C. for a constant weight.

[0009] Furthermore, the ratio of the FeCl2 / FeCl3 salt solution of the composite mixed solution is as follows: 2 g of FeCl2·4H2O and 3 g of FeCl3·6H2O are added to 40 mL of deionized water to obtain a first mixed solution; the first mixed solution is then mixed with 5 g of sludge-based activated carbon, stirred for 30 min, and then 20 mL of NH3·H2O solution is added to prepare a second mixed solution; the pH value of the second mixed solution is adjusted so that the iron salt forms a precipitate or complex, and then 20 mL of deionized water is added to prepare the composite mixed solution.

[0010] Furthermore, the composite mixed solution was continuously stirred for 30 min and then filtered through a sieve. The filtrate was rinsed with deionized water 5 times and then dried at 45° C. to a constant weight.

[0011] On the other hand, the present invention provides an application of a sludge-based magnetic activated carbon material. The sludge-based magnetic activated carbon material prepared according to the preparation method described above has an application in enhancing the methane production of excess sludge anaerobic digestion. The sludge-based magnetic activated carbon material prepared according to the preparation method described above is added to the excess sludge anaerobic digestion reactor, and the methane production is monitored in real time.

[0012] Furthermore, the excess sludge anaerobic digestion reactor is a fully automatic methane potential tester.

[0013] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0014] 1. The sludge-based magnetic activated carbon of the present invention helps to accelerate the hydrolysis and acidification rate of sludge, effectively promotes the hydrolysis and acidification process of organic matter, and can significantly enhance the degradation performance of substrates during anaerobic digestion. At the same time, the sludge-based magnetic activated carbon can significantly improve the degradation of organic matter in residual sludge and enhance sludge reduction.

[0015] 2. The sludge-based magnetic activated carbon with an appropriate concentration provided by the present invention can significantly improve the methane production kinetic parameters during the anaerobic digestion of excess sludge, while also improving the maximum biomethane production potential, peak biomethane production and the lag time of biomethane production to varying degrees.

[0016] 3. The presence of the sludge-based magnetic activated carbon of the present invention will significantly affect the generation and accumulation of ammonium nitrogen during anaerobic digestion and alleviate the inhibitory effect of ammonium nitrogen on the anaerobic digestion reaction of excess sludge.

[0017] 4. The method proposed in the present invention for enhancing the methane production performance of anaerobic digestion of excess sludge by using sludge-based magnetic activated carbon material is simple to operate, environmentally friendly, and can effectively improve the methane production efficiency of the anaerobic digestion reaction of excess sludge. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, constitute a part of this application, and do not constitute a limitation of the embodiments of the present invention. In the drawings:

[0019] Figure 1 This is a physical picture of the sludge-based magnetic activated carbon material provided in Example 1 of the present invention.

[0020] Figure 2 This is the cumulative methane production change curve provided in Example 2 of the present invention.

[0021] Figure 3 This is the cumulative methane production change curve provided in Example 3 of the present invention. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0023] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art to which this invention pertains. Although preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of this invention. All references mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related thereto. In the event of a conflict with any incorporated reference, the present specification controls. As used herein, the terms "including," "comprising," "having," "containing," and the like are open-ended, meaning to include, but not be limited to, the terms "a," "an," and "an" include plural references unless the context clearly indicates otherwise. It should be noted that the terms "first," "second," and the like are used solely for convenience of description and distinction and are not to be construed as indicating or implying relative importance. As used herein, the term "about" refers to a range of ±20% of the value that follows it. In some embodiments, the term "about" refers to a range of ±10% of the value that follows it. In some embodiments, the term "about" refers to a range of ±5% of the value that follows it.

[0024] Example 1

[0025] This embodiment discloses a method for preparing a sludge-based magnetic activated carbon material, comprising the following steps:

[0026] Step 1: The pretreated sludge was mixed with a 3 mol / L ZnCl2 activator solution at 30°C and a solid-liquid ratio of 1:2.5. After being immersed at room temperature for 24 h, the sludge was dried and then carbonized to prepare a sludge-based activated carbon substrate.

[0027] Specifically, step 1 specifically includes: the sludge in this application is sent to a sewage treatment plant, and the sludge is first naturally dried in a cool and ventilated place to a moisture content of 10%, and then the sludge is fully mixed with a 3 mol / L ZnCl2 (activator) solution at 30°C and a solid-liquid ratio of 1:2.5. After being immersed in room temperature for 24 hours, the immersed sludge is dried to constant weight in an oven at a temperature of 105°C. After the dried sludge is simply crushed, it is carbonized in a tubular resistance furnace at 600°C for 60 minutes, first soaked in a 3 mol / L HCl solution for 30 minutes, and then repeatedly rinsed with deionized water until neutral, and finally dried in an oven at 45°C to constant weight to obtain sludge-based activated carbon.

[0028] Step 2: adding the sludge-based activated carbon substrate to a composite mixed solution obtained by compounding a FeCl2 / FeCl3 salt solution and an NH3·H2O solution, and drying the solution to a constant weight after the reaction to obtain sludge-based magnetic activated carbon.

[0029] Specifically, the FeCl2 / FeCl3 salt solution ratio for the composite mixed solution is as follows: 2g of FeCl2·4H2O and 3g of FeCl3·6H2O are added to 40mL of deionized water to obtain a first mixed solution. The first mixed solution is then mixed with 5g of sludge-based activated carbon, stirred for 30 minutes, and then 20mL of NH3·H2O solution is added to prepare a second mixed solution. The pH of the second mixed solution is adjusted to form a precipitate or complex with the iron salt, and then 20mL of deionized water is added to prepare the composite mixed solution. Finally, the composite mixed solution is stirred continuously for 30 minutes and filtered through a mesh. The filtrate is rinsed with deionized water five times and then dried at 45°C to a constant weight to prepare the sludge-based magnetic activated carbon. Figure 1 A physical picture of sludge-based magnetic activated carbon prepared by the method in this example is shown.

[0030] Example 2

[0031] This embodiment discloses a method for enhancing the methane production performance of anaerobic digestion of excess sludge in a sewage treatment plant using the sludge-based magnetic activated carbon prepared in Example 1, and the steps are as follows:

[0032] 1) A strict anaerobic environment was established in a 550 mL anaerobic reaction bottle by purging with high-purity nitrogen (purity ≥99.99%) for 10 minutes. After adjusting the moisture content of excess sludge from a sewage treatment plant from 80% to 95%, a total of 500 mL (400 mL of substrate sludge and 100 mL of inoculum sludge) was added at a ratio of 4:1 (C / N ≈ 17-18) to the sludge. The pH of the mixture in the reaction bottle was adjusted to 6.9-7.1.

[0033] 2) Experimental groups were added with 0 g / L (R0), 4 g / L (R1), 8 g / L (R2), 12 g / L (R3), and 16 g / L (R4) of sludge-based magnetic activated carbon. The reaction temperature was set at (35.0 ± 0.5)°C and the stirring rate was (120 ± 5) rpm / min. Two replicates were set for each group.

[0034] 3) Record gas production in real time, and terminate the experiment when methane production is less than 10 mL / d for two consecutive days.

[0035] After 22 days of anaerobic digestion, the cumulative methane production of the control group (R0) was 689.25 mL. When the concentration of sludge-based magnetic activated carbon was 4, 8, 12, and 16 g / L, the cumulative methane production was 971.63 mL, 989.48 mL, 1051.78 mL, and 1005.37 mL, respectively, which were increased by 42.56%, 43.55%, 52.6%, and 45.86% compared with the control group. Figure 2 The graph shows the change curve of the cumulative methane production during the anaerobic digestion reaction of excess sludge in a sewage treatment plant by the sludge-based magnetic activated carbon in this embodiment.

[0036] Example 3

[0037] This embodiment discloses a method for enhancing the methane production performance of anaerobic digestion of excess sludge in a sewage treatment plant using the sludge-based magnetic activated carbon prepared in Example 1. The specific steps are as follows:

[0038] 1) A strict anaerobic environment was established in a 2-L anaerobic reaction bottle by purging with high-purity nitrogen (purity ≥99.99%) for 10 minutes. After adjusting the moisture content of excess sludge from a sewage treatment plant from 80% to 95%, 500 mL of the sludge (400 mL substrate sludge, 100 mL inoculum sludge) was added at a ratio of 4:1.

[0039] 2) Experimental groups were treated with 0 g / L (R0), 4 g / L (R1), 8 g / L (R2), 12 g / L (R3), and 16 g / L (R4) of sludge-based magnetic activated carbon, respectively. A 2 g / L NH₄⁺-N atmosphere (3.82 g of NH₄Cl was added to the reaction flask) was established. The reaction temperature was set at (35.0 ± 0.5)°C, and the stirring rate was (120 ± 5) rpm / min. Two replicates were prepared for each group.

[0040] 3) Replace 10 mL of the mixed solution every four days to maintain a constant sludge retention time. Record gas production in real time, and terminate the experiment when methane production is <10 mL / day for two consecutive days.

[0041] The cumulative methane production of the control group (R0) was 409.23 mL. When the concentration of sludge-based magnetic activated carbon was 4, 8, 12, and 16 g / L, the cumulative methane production in the reaction was 519.49, 551.63, 565.84, and 500.15 mL, respectively, which were 26.94%, 34.80%, 38.27%, and 22.22% higher than that of the control group. Figure 3 The graph shows the change curve of the cumulative methane production during the anaerobic digestion reaction of excess sludge in a sewage treatment plant by the sludge-based magnetic activated carbon in this embodiment.

[0042] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of 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 protection of the present invention.

Claims

1. A method for preparing sludge-based magnetic activated carbon material, characterized in that: The preparation method comprises: S100, mixing the pretreated sludge with a 3 mol / L ZnCl2 activator solution at 30° C. and a solid-liquid ratio of 1:2.5, and immersing the sludge at room temperature for 24 h, followed by drying and carbonization to prepare a sludge-based activated carbon substrate; S200, adding the sludge-based activated carbon substrate to a composite mixed solution obtained by compounding a FeCl2 / FeCl3 salt solution and an NH3·H2O solution, and drying to a constant weight after the reaction to obtain sludge-based magnetic activated carbon.

2. The method for preparing sludge-based magnetic activated carbon material according to claim 1, characterized in that: The sludge comes from a sewage treatment plant. The pretreatment includes: naturally drying the sludge to a moisture content of 10%.

3. The method for preparing sludge-based magnetic activated carbon material according to claim 1, characterized in that: The drying step is to dry the soaked sludge to a constant weight at 105°C. The carbonization process is to crush the sludge dried to a constant weight and then place it in a tubular resistance furnace at 600°C for 60 minutes. After carbonization, the samples were immersed in 3 mol / L HCl solution for 30 min, rinsed with deionized water until neutral, and finally dried at 45 °C to constant weight.

4. The method for preparing sludge-based magnetic activated carbon material according to claim 1, characterized in that: The ratio of the FeCl2 / FeCl3 salt solution of the composite mixed solution is to add 2g of FeCl2·4H2O and 3g of FeCl3·6H2O into 40 mL of deionized water to obtain a first mixed solution. Then, the first mixed solution was mixed with 5 g of sludge-based activated carbon, stirred for 30 min, and then 20 mL of NH3·H2O solution was added to prepare a second mixed solution; The pH value of the second mixed solution was adjusted to form a precipitate or a complex of the iron salt, and then 20 mL of deionized water was added to prepare a composite mixed solution.

5. The method for preparing sludge-based magnetic activated carbon material according to claim 4, characterized in that: The composite mixed solution was continuously stirred for 30 min and then filtered through a sieve. The filtrate was rinsed with deionized water 5 times and then dried at 45° C. to a constant weight.

6. An application of sludge-based magnetic activated carbon material, characterized in that: The use of the sludge-based magnetic activated carbon material prepared by the preparation method according to any one of claims 1 to 5 in enhancing the methane production by anaerobic digestion of excess sludge, The sludge-based magnetic activated carbon material prepared by the preparation method according to any one of claims 1 to 5 is added to a residual sludge anaerobic digestion reactor, and the methane generation is monitored in real time.

7. The use of the sludge-based magnetic activated carbon material according to claim 6, characterized in that: The excess sludge anaerobic digestion reactor is a fully automatic methane potential tester.

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