Method for enhancing the methanogenic efficiency of sludge anaerobic digestion by iron-based MOF

Abstract

The application discloses a method for enhancing the methanogenic efficiency of sludge anaerobic digestion by using an iron-based MOF, wherein conductive materials of 0, 100, 150 and 200 mg / g VS are added to a residual sludge system, and anaerobic digestion is carried out at a temperature of 37±1 DEG C and an initial pH of 7.0 for 30 days. The application first applies MIL-88A(Fe) to a residual sludge anaerobic digestion system, and MIL-88A(Fe) enhances the hydrolysis rate of organic matter and the methane production rate in the anaerobic digestion system. MIL-88A(Fe) mediates the DIET pathway by promoting the secretion of cytochrome C and the production of conductive pili in the anaerobic digestion system, thereby enhancing the electron transport capacity between microorganisms in the system. The application can improve the methane production, alleviate the accumulation and inhibition of volatile fatty acids, promote the acid production rate and the intracellular and extracellular electron transport rate in the anaerobic digestion process, enhance the in-situ conversion of CO2 in the anaerobic digestion system, improve the methane production rate, and provide a new idea for efficient resource utilization of residual sludge produced by a sewage biological treatment process and solid organic waste.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of organic waste resource utilization, and relates to a method for strengthening the methanogenic efficiency of sludge anaerobic digestion by an iron-based MOF. BACKGROUND

[0002] With the development of economy, the by-product waste activated sludge in the process of sewage treatment also increases year by year, but the sludge contains bacteria, pathogens, heavy metals and other toxic substances, which will pose a serious threat to the ecological environment and human health if not properly treated. On the other hand, due to its rich organic matter, chemical energy, nutrients and preferred low-cost biomass resources, waste activated sludge can be regarded as a valuable energy / resource storage, so the efficient resource utilization of waste activated sludge has become one of the focuses of effective disposal. Anaerobic digestion technology is a commonly used process for treating waste activated sludge, which has attracted widespread attention due to its high organic load, low energy consumption, high sludge reduction degree and production of methane and other energy gases. In the traditional anaerobic digestion process, due to the existence of organic matter in the cell or extracellular polymer, it is difficult for microorganisms to utilize and convert it into a substrate that can be utilized by methanogens, resulting in long process cycle and low methane yield in the traditional sludge anaerobic digestion process. Although a variety of sludge pretreatment methods including ultrasound, heat treatment, ozone, acid and alkali and other physical and chemical methods are introduced, these methods can improve the organic matter hydrolysis rate during anaerobic digestion to some extent and accelerate the subsequent methanogenesis process. However, the pretreated sludge still contains a large amount of organic matter that cannot be converted, and the produced biogas has high CO2 content and low heat value, so it is necessary to further strengthen the in-situ conversion of CO2 in the anaerobic digestion system. The introduction of conductive materials can promote the direct interspecies electron transfer (DIET) between methanogens and some mutualistic microorganisms relying on conductive materials, which is a more energy-efficient electron transfer method in the interspecies microbial metabolism process. Therefore, the introduction of conductive materials can promote the enrichment of methanogens and mutualistic microorganisms, which helps to improve the core competitiveness of methanogenesis and increase the methanogenesis rate and production rate by improving the energy metabolism in the methanogenesis process. Iron-based MOF (Metal-Organic Framework, metal-organic framework) materials are commonly used conductive materials for DIET pathway in anaerobic digestion system mediated methanogenesis process, which are applied in anaerobic digestion system in the form of Fe(0), Fe(II) and Fe(III). In the anaerobic digestion system, Fe(0), Fe(II) and Fe(III) provide electrons and reduce the redox potential, promoting the methane yield, but in the anaerobic digestion system, they are prone to aggregation and have poor stability, which inhibits electron transfer and reaction activity and limits their application. As an iron-based metal-organic framework material, MIL-88A(Fe) exhibits a highly ordered periodic arrangement structure, making its internal pore structure uniform and adjustable, and has the advantages of high porosity, functionalization, rich active sites, strong thermal and mechanical stability, etc., which has great development prospects in the field of excess sludge anaerobic digestion. SUMMARY

[0003] The present application aims to overcome the above-mentioned shortcomings of the prior art, and provides a method for strengthening the methane production efficiency of sludge anaerobic digestion by using an iron-based MOF, which can solve the problem of low methane production efficiency of residual sludge anaerobic digestion.

[0004] To achieve the above-mentioned purpose, the present application discloses a method for strengthening the methane production efficiency of sludge anaerobic digestion by using an iron-based MOF, comprising the following steps:

[0005] The waste activated sludge, inoculum and MIL-88A(Fe) are mixed, and then the pH value is adjusted to obtain an anaerobic digestion system, and then nitrogen gas is blown into the anaerobic digestion system until there is no oxygen in the anaerobic digestion system, and then the anaerobic digestion reaction is carried out under a closed condition to complete the iron-based MOF strengthened methane production efficiency of sludge anaerobic digestion.

[0006] The MIL-88A(Fe) with mesoporous structure provides conditions for the adhesion of microorganisms, and the functional groups on the surface are beneficial to the growth and reproduction of microorganisms, promote interspecies electron transfer, improve the transfer rate, accelerate sludge degradation and methane production, and improve the methane production.

[0007] The preparation process of the MIL-88A(Fe) is as follows:

[0008] FeCl3 and fumaric acid are dissolved in distilled water, and then stirred, and then subjected to a hydrothermal reaction to obtain MIL-88A(Fe).

[0009] The mass ratio of FeCl3 to fumaric acid is 0.580g:1.352g.

[0010] The temperature of the hydrothermal reaction is 65℃, the reaction time is 24h, and the stirring time is 12h.

[0011] The pH value is adjusted to 7.

[0012] The present application has the following beneficial effects:

[0013] The method for strengthening the methane production efficiency of sludge anaerobic digestion by using an iron-based MOF in the present application applies MIL-88A(Fe) to anaerobic digestion, strengthens the in-situ conversion of CO2 in the anaerobic digestion system, improves the methane production rate, breaks through the problems of long traditional anaerobic digestion period and low hydrolysis rate, is simple to operate, has strong processing capacity, and provides a good research foundation for the application of MOF in anaerobic digestion. At the same time, MIL-88A(Fe) mediates the DIET pathway by promoting the secretion of cytochrome C and the production of conductive pili in the anaerobic digestion system, thereby strengthening the electron transfer capacity between microorganisms in the system. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 The SEM image of the MIL-88A(Fe) material;

[0015] Figure 2 Structure diagram of anaerobic digestion methanogenic device for the method of the present application;

[0016] Figure 3 Cumulative methanogenic amount diagram of each treatment group in the anaerobic digestion methanogenic process. DETAILED DESCRIPTION

[0017] In order to better understand the technical scheme of the present application, the technical scheme in the embodiments of the present application will be described clearly and completely below in conjunction with the accompanying drawings of the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments, and are not intended to limit the scope of the present application. In addition, in the following description, the description of the known structures and technologies is omitted to avoid unnecessary confusion of the concepts disclosed in the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without making creative efforts should belong to the scope of protection of the present application.

[0018] The structural schematic diagrams according to the disclosed embodiments of the present application are shown in the accompanying drawings. These diagrams are not drawn to scale, in which some details are exaggerated for the purpose of clarity, and some details can be omitted. The shapes of various regions, layers and their relative sizes and positional relationships shown in the diagrams are only exemplary, and in actuality, there can be deviations due to manufacturing tolerances or technical limitations, and regions / layers with different shapes, sizes and relative positions can be additionally designed by those skilled in the art according to actual needs.

[0019] Embodiment one

[0020] The method for strengthening the sludge anaerobic digestion methanogenic efficiency by the iron-based MOF according to the present application comprises the following steps:

[0021] 1) Selecting sludge generated by a biological wastewater treatment process, concentrating the sludge by gravity settling for 12-24 h, removing the supernatant of the sludge, and then storing it in a refrigerator at 4℃ to obtain waste activated sludge;

[0022] 2) Preparing MIL-88A(Fe), specifically, dissolving 0.580 g of FeCl3 and 1.352 g of fumaric acid in distilled water, stirring for 12 h, obtaining a mixed solution, transferring the mixed solution to a polytetrafluoroethylene liner, and hydrothermal treatment at 65℃ for 24 h to obtain MIL-88A(Fe). MIL-88A(Fe) is sequentially washed with ethanol and water for three times each, and then dried in an oven at 60℃.

[0023] 3) The inoculation sludge for anaerobic digestion is taken from a laboratory-stable running anaerobic digestion reactor, with total solids of 1.63%, volatile solids of 1.31%, and waste activated sludge as the substrate for anaerobic digestion, wherein the total solids of the inoculation waste activated sludge are 4.17%, and the volatile solids are 2.92%.

[0024] 4) The digestion substrate and the inoculation sludge in the anaerobic digestion are mixed at a ratio of 2:1, and are placed in anaerobic fermentation bottles; MIL-88A(Fe) is added to the bottles at a dosage concentration of 0, 100, 150, and 200 mg / g VS; the pH in the anaerobic digestion system is adjusted to 7.0; the system is filled with nitrogen gas; the anaerobic conditions of the system are maintained; the anaerobic digestion bottles are placed in a constant-temperature water bath for anaerobic digestion and methane production test, at a temperature of 37±1℃, and are operated for 30 days; and no sludge is added or discharged during the experiment.

[0025] Example Two

[0026] This example is used as a comparative experiment, and the difference from Example One is that no MIL-88A(Fe) material is added, and the test results are as follows Figure 2 Compared with the system without adding any material (159±3 mL CH4 / g VS), after adding 150 mg / g VS MIL-88A(Fe), the cumulative methane production of the anaerobic digestion system is 250±4 mL CH4 / g VS, and the cumulative methane production and the daily maximum methane production are increased by 56.60% and 45.75% compared with the anaerobic digestion system without adding the material.

[0027] In the anaerobic digestion system, MIL-88A(Fe) promotes the secretion of cytochrome C and conductive pili, realizes efficient electron transfer between methanogens and acidogens, realizes rapid utilization of organic matter in sludge, alleviates the accumulation of volatile fatty acids in the system, avoids the problem of large energy consumption in interspecies electron transfer with H2 as the carrier, strengthens the in-situ conversion of CO2 in the anaerobic digestion system, and improves the methane production rate.

[0028] The present application has the following characteristics:

[0029] 1) Adding 150 mg / g VS MIL-88A(Fe) improves the hydrolysis and acidification rate of organic matter and the methane generation rate;

[0030] 2) The cumulative methane production and the daily maximum methane production of the system with 150 mg / g VS MIL-88A(Fe) are increased by 56.60% and 45.75% compared with the anaerobic digestion system without adding the material;

[0031] 3) The addition of 150 mg / g VS MIL-88A(Fe) accelerated the utilization of acetate by methanogens. Meanwhile, MIL-88A(Fe) improved the activities of key enzymes in anaerobic digestion, such as α-glucosidase, acetate kinase and F420, thus enhancing the methanogenic efficiency;

[0032] 4) The addition of 150 mg / g VS MIL-88A(Fe) promoted the secretion of reducing proteins in the system, enhanced the intracellular and extracellular electron transfer rates in the anaerobic digestion system, specifically the ability to accept and contribute electrons;

[0033] 5) MIL-88A(Fe) promoted the secretion of cytochrome C and conductive pili to achieve the transfer of electrons between acidogenic bacteria and methanogens, thus completing the DIET pathway;

[0034] 6) MIL-88A(Fe) mediated the growth of Methanobacterium and Methanosaeta in the anaerobic digestion system, and inhibited the growth of Candidatus-Methanofastidiosum, indicating that MIL-88A(Fe) mediated the acetate oxidation and carbon dioxide reduction methanogenesis pathway through the DIET pathway, and inhibited the hydrogenotrophic methanogenesis pathway.

[0035] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application and not to limit it. Although the present application has been described in detail with reference to the above examples, those skilled in the art should understand that the specific embodiments of the present application can be modified or replaced by equivalents without departing from the spirit and scope of the present application. Any modification or equivalent replacement without departing from the spirit and scope of the present application should be covered within the protection scope of the claims of the present application.

Claims

1. A method for enhancing the methanogenic efficiency of anaerobic digestion of sludge using iron-based MOFs, characterized in that, Includes the following steps: Waste activated sludge, inoculum, and MIL-88A(Fe) were mixed, and the pH was adjusted to obtain an anaerobic digestion system. Nitrogen gas was then introduced until there was no oxygen in the anaerobic digestion system. The anaerobic digestion reaction was then carried out under closed conditions to complete the iron-based MOF-enhanced sludge anaerobic digestion methanogenesis efficiency. MIL-88A(Fe), with its mesoporous structure, provides conditions for microbial attachment, and its surface functional groups are conducive to microbial growth and reproduction, promote interspecies electron transfer, increase its transfer rate, accelerate sludge degradation and methane production, and increase methane yield; The preparation process of MIL-88A(Fe) is as follows: FeCl3 and fumaric acid were dissolved in distilled water, stirred, and then subjected to a hydrothermal reaction to obtain MIL-88A(Fe).

2. The method for enhancing the methanogenic efficiency of anaerobic digestion of sludge using iron-based MOF according to claim 1, characterized in that, The mass ratio of FeCl3 to fumaric acid is 0.580 g: 1.352 g.

3. The method for enhancing the methanogenic efficiency of anaerobic digestion of sludge using iron-based MOF according to claim 1, characterized in that, The hydrothermal reaction temperature is 65℃.

4. The method for enhancing the methanogenic efficiency of anaerobic digestion of sludge using iron-based MOF according to claim 1, characterized in that, The reaction time is 24 hours.

5. The method for enhancing the methanogenic efficiency of anaerobic digestion of sludge using iron-based MOF according to claim 1, characterized in that, The stirring time is 12 hours.

6. The method for enhancing the methanogenic efficiency of anaerobic digestion of sludge using iron-based MOF according to claim 1, characterized in that, Adjust the pH to 7.

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