Method for promoting anaerobic production of methane from sludge by using tubular pore structure biochar

Abstract

The invention belongs to the technical field of sludge treatment and recycling, and relates to a method for promoting anaerobic methane production by sludge through tubular pore structure biochar. Comprising the following steps: screening, washing, segmenting and drying a biomass material with a natural grade pore network, and then pyrolyzing and screening to obtain tubular pore structure biochar; carrying out sedimentation, sieving, dilution and pyrohydrolysis on the residual sludge to obtain pretreated sludge; mixing the pretreated sludge with the inoculated sludge to obtain mixed sludge; and adding the tubular pore structure biochar and the mixed sludge into an anaerobic reactor, aerating nitrogen in the anaerobic reactor, sealing the anaerobic reactor in a water bath constant-temperature oscillator, and carrying out methane production until no methane is generated in the anaerobic reactor. According to the method, the anaerobic methanogenesis efficiency of the residual sludge is remarkably improved by utilizing the tubular pore structure biochar, and the improvement of the anaerobic methanogenesis efficiency of the sludge under the mediation of the exogenous conductive material is realized.

Description

Technical Field

[0001] This invention belongs to the field of sludge treatment and resource utilization technology, and relates to a method for promoting anaerobic methanogenesis in sludge using tubular porous biochar. Background Technology

[0002] Wastewater treatment plant sludge, a byproduct of wastewater treatment, contains 30%–50% of the pollutants in the wastewater, including organic pollutants, heavy metals, and microorganisms, posing a high risk of secondary pollution. Therefore, it is necessary to find suitable sludge treatment and disposal methods to achieve sludge reduction, stabilization, harmlessness, and resource recovery. Compared with other sludge treatment and disposal technologies, anaerobic methanogenesis is considered an important technological pathway for recovering energy from wastewater sludge in biological treatment technologies. Anaerobic methanogenesis can convert complex organic compounds in solid waste into renewable clean energy sources such as hydrogen and methane through biodegradation. Anaerobic digestion technology meets the sustainable development needs of wastewater sludge treatment and disposal, and is expected to achieve green and low-energy operation of wastewater treatment plants, thereby promoting the high-quality development of the wastewater treatment industry and demonstrating broad application prospects.

[0003] However, the practical application of anaerobic methanogenesis technology is still limited by its low methanogenesis efficiency. One of the most important reasons is the low efficiency of inter-species electron transfer (IET), which uses hydrogen and formic acid as electron transfer carriers, making it susceptible to the influence of the levels of hydrogen, formic acid, and short-chain fatty acids (SCFAs) during anaerobic methanogenesis. Furthermore, anaerobic methanogenesis has a long start-up time and poor operational stability.

[0004] Currently, a series of measures have been adopted to promote IET efficiency and improve system stability in anaerobic sludge digestion systems, thereby enhancing the system's methanogenic efficiency. For example, sludge pretreatment can accelerate the hydrolysis rate of sludge, increasing its conversion efficiency to macromolecular organic matter; optimizing system environmental conditions (such as pH, temperature, and redox potential) enhances microbial enzyme activity and metabolic efficiency, promoting the activity of key functional microbial communities (such as methanogens); adding conductive additives as electron mediators (such as granular activated carbon, magnetite, and biochar) accelerates electron transfer between acid-producing and methanogens, shortening metabolic pathways. Among these, conductive additives not only have the advantages of simple operation and low energy consumption, but their conductivity and good colonization space have also been proven to mediate IET and increase the abundance of functional microorganisms. Therefore, adding exogenous additives is an effective regulatory strategy to improve anaerobic methanogenic efficiency. Biochar, due to its abundant sources, low price, and good surface properties, is widely used in enhancing anaerobic methanogenic systems. However, due to differences in raw materials and preparation processes, biochar has complex physicochemical properties, which leads to different biochars having varying degrees of impact on the anaerobic methanogenesis efficiency of sludge. Summary of the Invention

[0005] To address the problem of low IET efficiency in existing anaerobic sludge digestion processes, this invention provides a method for promoting anaerobic methanogenesis in sludge using tubular porous biochar. The invention reveals the impact of tubular porous biochar on anaerobic methanogenesis in excess sludge, and demonstrates that tubular porous biochar significantly improves the efficiency of anaerobic methanogenesis in excess sludge. Furthermore, it achieves the enhancement of anaerobic methanogenesis efficiency in sludge mediated by exogenous conductive materials.

[0006] To achieve the above objectives, the present invention employs the following technical solution: This invention provides a method for promoting anaerobic methanogenesis in sludge using tubular porous biochar, comprising: Biomass materials with a natural hierarchical pore network are screened, washed, divided and dried, and then pyrolyzed and screened again to obtain tubular pore structure biochar. The remaining sludge is subjected to sedimentation, sieving, dilution and hot hydrolysis to obtain pretreated sludge; The pretreated sludge and the inoculated sludge are mixed to obtain mixed sludge; The tubular biochar and the mixed sludge are added to an anaerobic reactor. After aeration with nitrogen, the anaerobic reactor is sealed and placed in a water bath constant temperature shaker to produce methane until no more methane is generated in the anaerobic reactor.

[0007] Preferably, the mass ratio of the tubular porous biochar to the volatile suspended solids in the mixed sludge is 1:(8~10).

[0008] Preferably, the pyrolysis conditions are as follows: under anaerobic conditions, the temperature is increased to 750-800°C at a heating rate of 5-7°C / min, and pyrolyzed at 750-800°C for 2-3 hours, followed by cooling to room temperature at a rate of 5-7°C / min.

[0009] Preferably, the biomass material with a natural hierarchical pore network is lotus stem, corn husk, reed stalk, or sweet potato vine.

[0010] Preferably, the particle size of the tubular pore structure biochar is less than 0.15 mm.

[0011] Preferably, the settling time of the remaining sludge is not less than 24 hours.

[0012] Preferably, the remaining sludge is sieved through a 0.45~0.48mm screen.

[0013] Preferably, the conditions for the hot hydrolysis are: hot hydrolysis at 80~90℃ for no less than 30 minutes.

[0014] Preferably, the volume ratio of the pretreated sludge to the inoculated sludge is (9~10):1.

[0015] Preferably, the shaking speed of the water bath constant temperature oscillator is 120~130 rpm and the temperature is 35±1℃.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention enhances the anaerobic methanogenesis efficiency of sludge by adding tubular porous biochar. Firstly, the prepared biochar has a unidirectional tubular porous structure, exhibits alkalinity, and contains numerous oxygen-containing functional groups on its surface. As an electron mediator, it accelerates electron transfer between acid-producing and methanogenic bacteria, shortening the metabolic pathway. Furthermore, through the adsorption of biochar and the reaction of surface functional groups, ammonia nitrogen in the anaerobic methanogenesis system remains at a low level, maintaining system stability. Secondly, the tubular porous biochar lowers the electron transfer energy barrier, reduces extracellular electron transfer resistance through a conductive network, optimizes energy metabolism pathways, enhances the activity of key enzymes (such as proteases, coenzyme F420, and cytochromes), and accelerates the β-oxidation of SCFAs and methanogenesis-related reactions. In the presence of tubular porous biochar, it adsorbs free SCFAs, thereby shortening the mass transfer distance with symbiotic bacteria (such as hydrogen-producing and acetic-producing bacteria) and methanogenic bacteria, preventing substrate diffusion loss in solution. Meanwhile, biochar adsorbs only some, not all, of the SCFAs, and the free SCFAs and biochar have a synergistic promoting effect on the anaerobic methanogenesis process in sludge. Specifically, biochar adsorbs SCFAs, shortening the mass transfer distance between them and hydrolytic enzymes and functional bacteria, indirectly improving hydrolysis efficiency. At the same time, it reduces the electron competition between SCFAs and methanogens, enhances the electron transfer capacity between microbial species, and increases the cytochrome C content and coenzyme F420 activity of anaerobic microorganisms. This promotes the conversion of recalcitrant volatile fatty acids (VFAs) such as propionic acid into acetic acid, providing sufficient substrate for methanogens and ultimately improving the efficiency of anaerobic methanogenesis. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 Line graphs showing the cumulative methane content of each group in Examples 1-4 and Comparative Example 1 of the present invention; Figure 2 Line graphs showing the methane formation rates of each group in Examples 1-4 and Comparative Example 1 of the present invention; Figure 3 SEM image of the lotus stem; Figure 4 SEM image of corn stalk husk; Figure 5 SEM image of reed stalks; Figure 6 This is a SEM image of sweet potato vines. Detailed Implementation

[0019] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0020] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0021] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0022] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0023] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0024] The present invention will now be described in further detail with reference to the accompanying drawings: This invention provides a method for promoting anaerobic methanogenesis in sludge using tubular porous biochar, comprising: S1: Biomass materials with a natural hierarchical pore network are screened, washed, divided and dried, and then heated to 750-800℃ under anaerobic conditions at a heating rate of 5-7℃ / min, and pyrolyzed at 750-800℃ for 2-3 hours. Then, they are cooled to room temperature at a rate of 5-7℃ / min and sieved through a 100-mesh sieve to obtain tubular pore structure biochar with a particle size of less than 0.15mm.

[0025] Impurities in the biomass material are removed by sieving, surface dust is removed by washing with water, and the material is then segmented. Washing the biomass material removes dissolved ions, including dissolved salts and harmful ions such as sulfide and chloride ions. The washed biomass material is then dried at 80°C for at least 24 hours. The organic components in the biomass material are decomposed under anaerobic conditions at 750–800°C to generate tubular porous biochar (carbon-rich solid material), volatile gases, and liquid products. After cooling, the biochar is sieved through a 100-mesh sieve to obtain tubular porous biochar with a particle size less than 0.15 mm. Sieving the tubular porous biochar adjusts its particle size distribution, enabling more effective adsorption of harmful substances in the mixed sludge and reducing its impact on the activity of microorganisms in the anaerobic digestion system.

[0026] Among them, biomass materials with a natural hierarchical pore network include lotus stalks, corn husks, reed stalks, or sweet potato vines. For example... Figures 3-6 As shown, the surface morphology and pore structure of the four biomass raw materials exhibit significant differences. Lotus stalks, corn husks, and sweet potato vines show relatively smooth surface characteristics, which is conducive to the formation of a uniform carbon skeleton during pyrolysis. Reed stalks, on the other hand, show a distinctly rough surface; this irregular morphology stems from their complex lignin and cellulose composite structure, providing more active sites for microbial attachment. Regarding pore structure, lotus stalks and corn husks have similar single-channel pores with relatively uniform pore size distribution, indicating relatively unobstructed internal mass transfer channels. While sweet potato vines have larger single-channel sizes, their pore density is significantly lower than other materials, which to some extent limits their specific surface area and adsorption capacity. Reed stalks exhibit the richest multi-level pore system, with a unique layered structure: an inner layer of large-diameter channels and an outer layer of small-diameter networks, forming a natural gradient mass transfer system. This structure not only greatly increases the specific surface area but also provides optimized space for substrate diffusion and microbial colonization.

[0027] Tubular-porous biochar, through its hierarchical pore size distribution (coexistence of micropores, mesopores, and macropores) and layered pore morphology, constructs a hierarchical and ordered enrichment, transport, and reaction system at the microscale, significantly optimizing the spatial configuration of microorganisms, substrates, and electrons. Functionally, macropores act as rapid channels for transporting large organic molecules, mesopores selectively enrich short-chain fatty acids, and micropores adsorb small-molecule metabolites, forming a substrate concentration gradient for targeted supply to methanogens. Regarding microbial colonization, hydrolytic bacteria (such as Firmicutes) are enriched in macropores, while electroactive bacteria (such as Clostridium) and methanogens (such as Methanosaeta) are mainly enriched in mesopores / micropores, forming a targeted match between pore size and functional microbial communities, achieving spatial coupling of functional microbial communities. Furthermore, the layered pores of tubular-porous biochar, combined with high specific surface area and surface functional groups, construct electron transport pathways and local reaction sites, promoting direct interspecies electron transfer (DIET).

[0028] Tubular-porous biochar achieves efficient conversion and composition optimization of SCFAs through its unique continuous hierarchical pore system and directional transport channels. On the one hand, macropores act as rapid transport channels, accelerating the entry of large molecular substrates such as polysaccharides and proteins into the pore interior, where they are preferentially degraded by hydrolytic bacteria colonizing the pore entrance. On the other hand, mesopores selectively enrich intermediate products (such as propionic acid and butyric acid) and promote the conversion of these into readily available substrates such as acetic acid by acidifying bacteria through their exposed oxygen-containing functional groups with high specific surface area. Simultaneously, micropores adsorb and concentrate small molecule acetic acid, directly connecting with methanogenic bacteria colonizing the micropore interface, forming a continuous metabolic pathway of "hydrolysis-acidification-methanogenesis". This structure allows functional bacterial communities at different metabolic stages to colonize separately in the hierarchical pores, avoiding substrate competition inhibition and promoting the optimization of SCFA composition towards acetic acid dominance. Non-tubular or homogeneous porous biochars (such as granular char) cannot achieve this effect because the uniform pore size leads to the mixing and accumulation of large molecular substrates and small molecule metabolites, increasing diffusion resistance. Furthermore, the disordered and mixed colonization of functional bacteria reduces metabolic efficiency; for example, hydrolyzing bacteria and acid-producing bacteria compete for colonization space. In addition, the inability to form an acetic acid concentration gradient leads to the accumulation of recalcitrant SCFAs such as propionic acid. Therefore, the continuous pore size gradient and directional channels of the tubular structure are crucial for achieving efficient metabolism, a key advantage that disordered porous materials cannot replicate.

[0029] S2: Settle the remaining sludge for no less than 24 hours. The remaining sludge is then sieved through a 0.45~0.48mm screen, diluted, and then hydrolyzed at 80~90℃ for no less than 30 minutes to obtain pretreated sludge.

[0030] The excess sludge is treated through sedimentation, sieving, dilution, and hot water hydrolysis. Sieving through a 0.45~0.48mm screen effectively removes sand, fibers, and other large, inert particles from the sludge, significantly reducing the adverse effects of these inorganic and recalcitrant organic substances on the subsequent anaerobic digestion process. Simultaneously, hot water hydrolysis disrupts the structure of the excess sludge, releasing more dissolved organic matter and creating more favorable substrate conditions for subsequent methane production.

[0031] S3: Mix the pretreated sludge and the inoculated sludge at a volume ratio of (9~10):1 to obtain mixed sludge.

[0032] Inoculation sludge refers to activated sludge containing a large number of highly efficient anaerobic microorganisms (including hydrolytic bacteria, acid-producing bacteria, and especially methanogenic archaea) that is artificially added when starting a new anaerobic digester. Inoculation sludge is rich in anaerobic functional microorganisms capable of degrading organic matter. After being mixed with pretreated sludge, it can quickly adapt to the environment and begin degrading the organic matter in the sludge, ultimately converting it into methane.

[0033] S4: Tubular porous biochar and mixed sludge are added to the anaerobic reactor, wherein the mass ratio of volatile suspended solids in the tubular porous biochar to that in the mixed sludge is 1:(8~10). After aeration with nitrogen, the anaerobic reactor is sealed and placed in a water bath constant-temperature shaker to produce methane until no more methane is generated in the anaerobic reactor. The shaking speed of the water bath constant-temperature shaker is 120~130 rpm, and the temperature is 35±1℃. Under anaerobic conditions, anaerobic microorganisms produce methane by decomposing complex organic matter (such as organic matter in the mixed sludge).

[0034] By mixing tubular-porous biochar with mixed sludge, the biochar provides more attachment sites for microorganisms in the system, promoting the aggregation of methanogens and symbiotic bacteria, forming a highly efficient metabolic microenvironment. Furthermore, under the catalytic action of the tubular-porous biochar, anaerobic microorganisms can more effectively convert organic matter into methane, increasing the efficiency and rate of methane production. The tubular-porous biochar prepared in this invention has a unidirectional tubular-porous structure and is alkaline. Its surface is rich in oxygen-containing functional groups and possesses excellent capacitance characteristics, significantly enhancing its electron transport capacity. In addition, through the adsorption of the tubular-porous biochar and the reaction of its surface functional groups, ammonia nitrogen in the anaerobic methanogenesis system remains at a low level, maintaining system stability. On the other hand, the addition of tubular-porous biochar increases the activity of proteases, coenzyme F420, and the INT-Electron Transport System (INT-ETS), further promoting interspecies electron transport processes among microorganisms. Tubular biochar from different biomass sources selectively enriched relevant hydrolytic and acidifying bacteria, enhancing the hydrolysis and acidification stages, accelerating the conversion of SCFAs and optimizing their composition, thus providing sufficient substrates for methanogenesis. Furthermore, it modulated the structural composition of the methanogenic community, increasing the abundance of electroactive methanogens (such as *Methanobacterium*, *Methanosaeta*, and *Methanosarcina*), thereby enhancing the single methanogenesis pathway and the DIET process.

[0035] Furthermore, tubular-porous biochar can increase the accumulation of humic acids in the extracellular polymeric layer, promoting extracellular electron transport. As an electron mediator, tubular-porous biochar can accelerate electron transport between acid-producing and methanogenic bacteria, shortening metabolic pathways. Simultaneously, it lowers the electron transport energy barrier, reducing extracellular electron transfer resistance through a conductive network, optimizing energy metabolism pathways, enhancing the activity of key enzymes (such as coenzyme F420 and cytochromes), and accelerating β-oxidation of SCFAs and methanogenesis-related reactions. In the presence of tubular-porous biochar, it adsorbs free SCFAs, thereby shortening the mass transfer distance with symbiotic bacteria (such as hydrogen-producing and acetic-producing bacteria) and methanogenic bacteria, avoiding substrate diffusion loss in solution. Moreover, tubular-porous biochar adsorbs only some, not all, of the SCFAs, and the free SCFAs and tubular-porous biochar have a synergistic promoting effect on the anaerobic methanogenesis process in sludge. Specifically, the tubular porous structure of biochar adsorbs SCFAs, shortening the mass transfer distance between them and hydrolytic enzymes and functional bacterial communities, thus indirectly improving hydrolysis efficiency. Simultaneously, it reduces electron competition between SCFAs and methanogens, enhances interspecies electron transfer, and increases the cytochrome C content and coenzyme F420 activity of anaerobic microorganisms. This promotes the conversion of recalcitrant VFAs such as propionic acid into acetic acid, providing ample substrate for methanogens and ultimately improving anaerobic methanogenesis efficiency.

[0036] In summary, this invention utilizes tubular biochar formed by the pyrolysis of biomass materials with a natural hierarchical pore network. Its unique pore network and surface characteristics provide ideal attachment sites for microorganisms and act as an electron transport bridge to promote direct interspecies electron transfer. Through a combination of physical and thermal processes, the structure of sludge flocs is broken down, releasing organic matter and removing inhibitors, significantly improving substrate bioavailability. The introduction of inoculated sludge constructs a functional microbial community, forming a synergistic system of "conductive network-functional microbial community" with the biochar. Finally, in a strictly anaerobic environment, the biochar shortens the substrate mass transfer distance through adsorption and enrichment effects, optimizes the microenvironment of microbial metabolism, and simultaneously promotes the coupling of organic matter hydrolysis and acidification with methanation processes, thereby achieving an overall improvement in methanogenesis efficiency.

[0037] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0038] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" refers to weight percentage, "parts" refers to parts by weight, and "ratio" refers to weight proportion.

[0039] Example 1 Impurities were removed by manual sieving of the lotus stems; surface dust was removed by washing with water and the stems were then divided; the washed lotus stem material was dried at 80℃ for 24 hours; the dried lotus stem material was then heated to 750℃ at a rate of 5℃ / min under anaerobic conditions and pyrolyzed for 2 hours, and then cooled to room temperature at a rate of 5℃ / min. Finally, the material was sieved through a 100-mesh sieve to obtain tubular pore structure biochar with a particle size of less than 0.15 mm. The remaining sludge was allowed to settle naturally for 24 hours. The settled sludge was then sieved through a 0.45 mm sieve to remove sand, gravel, and large particles. The sieved sludge was diluted to a suspended solids concentration of 8000 mg / L and then subjected to hot hydrolysis at 80°C for 30 minutes to obtain pretreated sludge. The pretreated sludge and inoculated sludge were mixed at a volume ratio of 9:1 to obtain mixed sludge. Tubular biochar and mixed sludge were added to an anaerobic reactor, with a volatile suspended solids (VSS) mass ratio of 1:8 between the two. After aeration with nitrogen for 5 minutes, the anaerobic reactor was sealed and placed in a water bath at 35°C with a shaking speed of 120 rpm. Methane production continued until no more methane was generated in the anaerobic reactor. The cumulative methane accumulation was 178.9 mL CH4 / gVSS, and the maximum daily methane production rate was 20.6 mL / d.

[0040] Example 2 The corn stalks were manually sieved to remove impurities; the surface dust was removed by washing with water and then the material was divided; the washed lotus stalks were dried at 80℃ for 25 hours; the dried lotus stalks were heated to 750℃ at a heating rate of 5℃ / min under anaerobic conditions and pyrolyzed for 2 hours, then cooled to room temperature at a rate of 5℃ / min, and then sieved with a 100-mesh sieve to obtain tubular pore structure biochar with a particle size of less than 0.15mm. The remaining sludge was allowed to settle naturally for 24 hours. The settled sludge was then sieved through a 0.45 mm sieve to remove sand, gravel, and large particles. The sieved sludge was diluted to a suspended solids concentration of 8000 mg / L and then subjected to hot hydrolysis at 80°C for 30 minutes to obtain pretreated sludge. The pretreated sludge and inoculated sludge were mixed at a volume ratio of 9:1 to obtain mixed sludge. Tubular biochar and mixed sludge were added to an anaerobic reactor, with a volatile suspended solids (VSS) mass ratio of 1:8 between the two. After aeration with nitrogen for 5 minutes, the anaerobic reactor was sealed and placed in a water bath at 35°C with a shaking speed of 120 rpm. Methane production continued until no more methane was generated in the anaerobic reactor. The cumulative methane accumulation was 176.9 mL CH4 / gVSS, and the maximum daily methane production rate was 20.4 mL / d.

[0041] Example 3 Impurities were removed by manual sieving of reed stalks; surface dust was removed by washing with water and the reed stalks were then divided; the washed reed stalks were dried at 80℃ for 26 hours; the dried reed stalks were then heated to 750℃ at a rate of 5℃ / min under anaerobic conditions and pyrolyzed for 3 hours, and then cooled to room temperature at a rate of 5℃ / min. Finally, the reed stalks were sieved through a 100-mesh sieve to obtain tubular pore structure biochar with a particle size of less than 0.15 mm. The remaining sludge was allowed to settle naturally for 26 hours. The settled sludge was then sieved through a 0.45 mm sieve to remove sand, gravel, and large particles. The sieved sludge was diluted to a suspended solids concentration of 8000 mg / L and then subjected to hot hydrolysis at 80°C for 35 minutes to obtain pretreated sludge. The pretreated sludge and inoculated sludge were mixed at a volume ratio of 9:1 to obtain mixed sludge. Tubular biochar and mixed sludge were added to an anaerobic reactor, with a volatile suspended solids (VSS) mass ratio of 1:8. After aeration with nitrogen for 6 minutes, the anaerobic reactor was sealed and placed in a water bath at 34°C with a shaking speed of 130 rpm. Methane production continued until no more methane was generated in the anaerobic reactor. The cumulative methane accumulation was 183.9 mL CH4 / g VSS, and the maximum daily methane production rate was 19.4 mL / d.

[0042] Example 4 The sweet potato vines were manually sieved to remove impurities; the surface dust was removed by washing with water and then the vines were divided; the washed vines were dried at 80°C for 27 hours; the dried vines were then heated to 750°C at a rate of 5°C / min under anaerobic conditions and pyrolyzed for 3 hours, and then cooled to room temperature at a rate of 5°C / min. Finally, the vines were sieved through a 100-mesh sieve to obtain tubular pore structure biochar with a particle size of less than 0.15 mm. The remaining sludge was allowed to settle naturally for 26 hours. The settled sludge was then sieved through a 0.46 mm sieve to remove sand, gravel, and large particles. The sieved sludge was diluted to a suspended solids concentration of 8000 mg / L and then subjected to hot hydrolysis at 80°C for 40 minutes to obtain pretreated sludge. The pretreated sludge and inoculated sludge were mixed at a volume ratio of 9:1 to obtain mixed sludge. Tubular biochar and mixed sludge were added to an anaerobic reactor, with a volatile suspended solids (VSS) mass ratio of 1:8 between the two. After aeration with nitrogen for 6 minutes, the anaerobic reactor was sealed and placed in a water bath at a constant temperature of 36°C and a shaking speed of 125 rpm for methane production until no more methane was generated. The cumulative methane accumulation was 171.6 mL CH4 / g VSS, and the maximum daily methane production rate was 19.8 mL / d.

[0043] Example 5 Impurities were removed by manual sieving of the lotus stems; surface dust was removed by washing with water and the stems were then divided; the washed lotus stem material was dried at 80℃ for 27 hours; the dried lotus stem material was then heated to 800℃ at a rate of 7℃ / min under anaerobic conditions and pyrolyzed for 3 hours, and then cooled to room temperature at a rate of 7℃ / min. Finally, the material was sieved through a 100-mesh sieve to obtain tubular pore structure biochar with a particle size of less than 0.15 mm. The remaining sludge was allowed to settle naturally for 28 hours. The settled sludge was then sieved through a 0.48 mm sieve to remove sand, gravel, and large particles. The sieved sludge was diluted to a suspended solids concentration of 8000 mg / L and then subjected to hot hydrolysis at 85°C for 30 minutes to obtain pretreated sludge. The pretreated sludge and inoculated sludge were mixed at a volume ratio of 10:1 to obtain mixed sludge. Tubular biochar and mixed sludge were added to an anaerobic reactor, with a volatile suspended solids (VSS) mass ratio of 1:9 between the two. After aeration with nitrogen for 8 minutes, the anaerobic reactor was sealed and placed in a water bath at a constant temperature of 35°C and a shaking speed of 123 rpm for methane production until no more methane was generated. The cumulative methane accumulation was 179.8 mL CH4 / gVSS, and the maximum daily methane production rate was 21.0 mL / d.

[0044] Example 6 Impurities were removed by manual sieving of reed stalks; surface dust was removed by washing with water and the reed stalks were then divided; the washed reed stalks were dried at 80℃ for 27 hours; the dried reed stalks were then heated to 800℃ at a rate of 7℃ / min under anaerobic conditions and pyrolyzed for 3 hours, and then cooled to room temperature at a rate of 7℃ / min. Finally, the reed stalks were sieved through a 100-mesh sieve to obtain tubular pore structure biochar with a particle size of less than 0.15 mm. The remaining sludge was allowed to settle naturally for 30 hours. The settled sludge was then sieved through a 0.45 mm sieve to remove sand, gravel, and large particles. The sieved sludge was diluted to a suspended solids concentration of 8000 mg / L and then subjected to hot hydrolysis at 90°C for 30 minutes to obtain pretreated sludge. The pretreated sludge and inoculated sludge were mixed at a volume ratio of 10:1 to obtain mixed sludge. Tubular biochar and mixed sludge were added to an anaerobic reactor, with a volatile suspended solids (VSS) mass ratio of 1:10 between the two. After aeration with nitrogen for 8 minutes, the anaerobic reactor was sealed and placed in a water bath at a constant temperature of 36°C and a shaking speed of 128 rpm for methane production until no more methane was generated. The cumulative methane accumulation was 184.6 mL CH4 / g VSS, and the maximum daily methane production rate was 20.1 mL / d.

[0045] Comparative Example 1 The remaining sludge was allowed to settle naturally for 24 hours. The settled sludge was then sieved through a 0.45 mm sieve to remove sand, gravel, and large particles. The sieved sludge was diluted to a suspended solids concentration of 8000 mg / L and then subjected to hot hydrolysis at 80°C for 30 minutes to obtain pretreated sludge. The pretreated sludge and inoculated sludge were mixed at a volume ratio of 9:1 to obtain mixed sludge. Mixed sludge was added to the anaerobic reactor. After aeration with nitrogen for 5 minutes, the anaerobic reactor was sealed and placed in a water bath constant-temperature shaker at a shaking speed of 120 rpm and a temperature of 35°C to produce methane until no more methane was generated in the anaerobic reactor. The cumulative methane accumulation was 156.4 mL CH4 / gVSS, and the maximum daily methane production rate was 18.5 mL / d.

[0046] like Figure 1 As shown, the methane accumulation in Comparative Example 1 was 156.4 mL CH4 / gVSS, while the methane accumulation in Examples 1-4 of this invention were 178.9 mL CH4 / gVSS, 176.9 mL CH4 / gVSS, 183.9 mL CH4 / gVSS, and 171.6 mL CH4 / gVSS, respectively, which were 14.4%, 13.1%, 17.6%, and 9.7% higher than that in Comparative Example 1, respectively. This indicates that the tubular porous biochar structure promoted the anaerobic methanogenesis process.

[0047] To further reveal the impact of tubular porous biochar on anaerobic methanogenesis systems in sludge, the methanogenesis rate was further analyzed, such as... Figure 2 The figure shows line graphs of methane production rates for Examples 1-4 and Comparative Example 1. It can be seen that the methane production rates of Examples 1-4 are significantly higher than those of Comparative Example 1. Furthermore, Examples 1-4 and Comparative Example 1 all reached their maximum daily methane production rate on day 8. The maximum daily methane production rates of Examples 1-4 were 20.6 mL / d, 20.4 mL / d, 19.4 mL / d, and 19.8 mL / d, respectively, while the maximum daily methane production rate of Comparative Example 1 was 18.5 mL / d. In addition, compared to the lag period of 3.4 days in Comparative Example 1, the lag periods of methane production in Examples 1-4 were shortened to 3.0, 2.9, 3.0, and 2.8 days, respectively. This indicates that tubular porous biochar can accelerate the methane production efficiency of anaerobic methanogenesis. This is because tubular porous biochar has a good pore structure and surface properties, which can provide a suitable environment for functional microorganisms and can also act as a carrier for direct electron transfer between microbial species, promoting interspecies metabolic processes.

[0048] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for promoting anaerobic methanogenesis from sludge using tubular porous biochar, characterized in that, include: Biomass materials with a natural hierarchical pore network are screened, washed, divided and dried, and then pyrolyzed and screened again to obtain tubular pore structure biochar. The remaining sludge is subjected to sedimentation, sieving, dilution and hot hydrolysis to obtain pretreated sludge; The pretreated sludge and the inoculated sludge are mixed to obtain mixed sludge; The tubular biochar and the mixed sludge are added to an anaerobic reactor. After aeration with nitrogen, the anaerobic reactor is sealed and placed in a water bath constant temperature shaker to produce methane until no more methane is generated in the anaerobic reactor.

2. The method for promoting anaerobic methanogenesis from sludge using tubular porous biochar according to claim 1, characterized in that, The mass ratio of the tubular biochar to the volatile suspended solids in the mixed sludge is 1:(8~10).

3. The method for promoting anaerobic methanogenesis from sludge using tubular porous biochar according to claim 1, characterized in that, The pyrolysis conditions are as follows: under anaerobic conditions, the temperature is increased to 750-800℃ at a heating rate of 5-7℃ / min, and then pyrolyzed at 750-800℃ for 2-3 hours, followed by cooling to room temperature at a rate of 5-7℃ / min.

4. The method for promoting anaerobic methanogenesis from sludge using tubular porous biochar according to claim 1, characterized in that, The biomass material with a natural hierarchical pore network is lotus stem, corn husk, reed stalk, or sweet potato vine.

5. The method for promoting anaerobic methanogenesis from sludge using tubular porous biochar according to claim 1, characterized in that, The tubular pore structure biochar has a particle size of less than 0.15 mm.

6. The method for promoting anaerobic methanogenesis from sludge using tubular porous biochar according to claim 1, characterized in that, The settling time of the remaining sludge shall not be less than 24 hours.

7. The method for promoting anaerobic methanogenesis from sludge using tubular porous biochar according to claim 1, characterized in that, The remaining sludge is sieved through a 0.45~0.48mm screen.

8. The method for promoting anaerobic methanogenesis in sludge using tubular porous biochar according to claim 1, characterized in that, The conditions for the hot hydrolysis are: hot hydrolysis at 80~90℃ for no less than 30 minutes.

9. The method for promoting anaerobic methanogenesis from sludge using tubular porous biochar according to claim 1, characterized in that, The volume ratio of the pretreated sludge to the inoculated sludge is (9~10):

1.

10. A method for promoting anaerobic methanogenesis in sludge using tubular porous biochar according to claim 1, characterized in that, The shaking speed of the water bath constant temperature oscillator is 120~130 rpm, and the temperature is 35±1℃.

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