A closed-loop processing utilization method for biogas residue based on gas-carbon co-production

Abstract

The present application relates to a kind of closed loop processing and utilization method of biogas residue based on gas-carbon coproduction, belong to organic solid waste processing field.Closed loop processing and utilization method includes the following steps: S1, biogas residue is mixed with raw material water, by hydrothermal carbonization technology, obtain hydrothermal carbonization wastewater and hydrothermal carbon;S2, hydrothermal carbonization wastewater is mixed with hydrothermal carbon, anaerobic fermentation, obtain biogas and fermentation product;S3, fermentation product is centrifuged, obtain supernatant, and the supernatant is recycled for S1, and solid remainder is recycled for S2;S1 biogas residue is obtained by acid production fermentation.Adopt biogas residue as raw material and carry out hydrothermal carbonization processing;Residual organic acid in the remainder after acid production fermentation, in the process of hydrothermal carbonization, residual organic acid promotes the depolymerization of not completely degraded lignocellulose, so that the performance of the obtained product hydrothermal carbon is improved.The present application can convert and utilize the effective carbon source components in hydrothermal carbonization aqueous phase byproduct, and recover the energy contained in biogas residue to the maximum extent.

Description

Technical Field

[0001] This invention belongs to the field of organic solid waste treatment, specifically relating to a closed-loop treatment and utilization method for biogas residue based on gas-carbon cogeneration. Background Technology

[0002] Straw, as an organic solid waste from agricultural production, is now widely used in biogas production. However, the lignocellulose component of straw is difficult to completely degrade after fermentation, and a large amount of solid fermentation residue, namely biogas residue, remains after solid-liquid separation of fermentation liquid. The treatment and utilization of biogas residue is of great significance to the economics of the entire biogas process.

[0003] Hydrothermal carbonization (HTC) technology can convert biomass into carbon-based materials with specific physicochemical structures, such as porosity and pore size, under certain temperatures (180-250℃) and autogenous pressure. There are numerous reports on the hydrothermal carbonization of biomass raw materials. For example, Falco and Ledesma produced hydrothermal carbon from rye straw and walnut shells; Yu et al. obtained hydrothermal carbon from fruit shells with a yield of 31.4% and an HHV (higher heating value) of 25.8 MJ / kg. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a closed-loop treatment and utilization method for biogas residue based on gas-carbon cogeneration, develops a biogas residue utilization pathway based on energy recovery, and realizes the recycling of main and by-product systems.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] A closed-loop treatment and utilization method for biogas residue based on gas-coke cogeneration includes the following steps:

[0007] S1. The biogas residue is mixed with the raw water and subjected to hydrothermal carbonization technology to obtain hydrothermal carbonization wastewater and hydrothermal carbon.

[0008] S2. Mix hydrothermal carbonization wastewater with hydrothermal carbon and carry out anaerobic fermentation to obtain biogas and fermentation products;

[0009] S3. Centrifuge the fermentation material to obtain the supernatant. Use the supernatant as raw water in S1. Use the solid fermentation residue obtained by centrifugation as inoculum for domestication in S2.

[0010] The biogas residue in S1 is obtained through acid-producing fermentation.

[0011] Optionally, the raw material for acid-producing fermentation is silage straw and / or dry straw;

[0012] The method of acid-producing fermentation is as follows: silage straw is mixed with anaerobic granular sludge. In the initial stage of the reaction of the mixture, the pH is adjusted to 8, and acid production begins through percolation. The fermentation temperature is maintained at a mesophilic temperature of 38°C, and the retention time is 7 days. The solid residue of acid-producing fermentation is biogas residue.

[0013] The VS ratio of silage straw to anaerobic granular sludge was 4:1. The pH of the leachate was controlled every 4 hours throughout the process, and the pH of the leachate was always kept at the initial value.

[0014] Optionally, in S1, the biogas residue is mixed evenly with the raw water and then placed in a high-pressure reactor. The reaction temperature is 210℃ and the reaction time is 4h. The solid-liquid mixture is collected, filtered, and separated to obtain hydrothermal carbonization wastewater and hydrothermal carbon.

[0015] The solid-liquid mass ratio of biogas residue to raw water is 50:500.

[0016] Optionally, in S2, anaerobic granular sludge is added as an inoculum, mixed with hydrothermal carbonization wastewater and hydrothermal carbon, and fermented at 38°C to collect biogas and fermentation products.

[0017] Inoculum is mainly used to degrade and transform organic components; domesticated inoculum can adapt to changes in substrate components, forming a microbial community that is more conducive to the transformation of target products, thereby improving its ability to degrade substrates and its tolerance to recalcitrant organic matter.

[0018] The beneficial effects of this invention are as follows:

[0019] 1. When using biogas residue as raw material for hydrothermal carbonization, the specific surface area of ​​hydrothermal carbon is increased by approximately 50% compared to using raw agricultural waste. Simultaneously, if the residue from acid-producing fermentation contains a certain amount of residual organic acids, these residual organic acids promote the depolymerization of incompletely degraded lignocellulose during hydrothermal carbonization, further increasing the porosity of the hydrothermal carbon and thus further improving the performance of the obtained hydrothermal carbon product.

[0020] 2. Since biogas residue contains more than 70% moisture, hydrothermal carbonization technology is more suitable for processing materials with high moisture content than dry materials. From an energy perspective, hydrothermal carbonization technology not only reduces the additional energy input caused by moisture evaporation, but also produces hydrothermal carbon with a higher carbon content and improved calorific value after dehydration and decarboxylation reactions.

[0021] 3. Hydrothermal carbonization wastewater can undergo anaerobic fermentation independently. After adding hydrothermal carbon, it plays a crucial role in the anaerobic fermentation system. It can act as an adsorbent material, immobilizing microorganisms to enhance their tolerance to characteristic pollutants in the wastewater and improving their adsorption of recalcitrant organic matter. Furthermore, it can act as an electron transport carrier, increasing the electron transfer efficiency in the redox reaction process, promoting the effective conversion of organic acids to methane during anaerobic fermentation, and further increasing methane yield.

[0022] 4. After anaerobic fermentation, most of the biodegradable components in the hydrothermal carbonization wastewater are utilized (COD removal rate is 68.0%). However, a small amount of recalcitrant pollutants are still retained in the fermentation liquid. This part of the fermentation liquid needs to be properly treated to avoid secondary pollution. Therefore, from the perspective of recycling, it can be used as a reaction medium for the hydrothermal carbonization process of biogas residue. This not only reduces the addition of external fresh water, but also allows the recalcitrant pollutants to participate in the carbonization reaction again, consume the recalcitrant organic matter, and improve the carbonization yield.

[0023] 5. This invention can convert and utilize the effective carbon source components in the aqueous phase by-products of hydrothermal carbonization, maximize the recovery of energy contained in the biogas residue, and further broaden the utilization pathways of fermentation residues; through the organic combination of thermal and biochemical methods, it realizes the closed-loop treatment of biogas residue and the carbon cycle of the entire process. The energy utilization method of gas-carbon cogeneration provides a new idea and technical path for the comprehensive treatment of biogas residue. Detailed Implementation

[0024] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0025] The reagents and raw materials used in this invention can all be purchased through conventional channels. Unless otherwise specified, the reagents and raw materials used in this invention shall be used in accordance with conventional methods in the art or according to the product instructions. Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to the methods of this invention. The preferred embodiments and materials described herein are for illustrative purposes only.

[0026] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0027] Comparison of hydrothermal carbonization effects of different raw materials:

[0028] Experiment 1:

[0029] (1) The anaerobic granular sludge was taken from a sewage treatment plant in Shandong Province. The total solids (TS) content was 18.4% and the volatile solids (VS) content was 89.2% (-TS).

[0030] (2) Mix silage straw, anaerobic granular sludge and water evenly and then produce acid fermentation.

[0031] Specifically, the VS ratio of silage straw to sludge is 4:1; in the initial stage of the reaction of the mixture, the pH is adjusted to 8 with 6 mol / L NaOH solution, and the peristaltic pump is started to drive the leachate from the top down of the leachate bed device of the LBR device (landfill leachate biochemical device) to produce acid; the pH value of the leachate is measured every 4 hours, and the acidity and alkalinity of the leachate are controlled by 6 mol / L NaOH solution or 6 mol / L HCl solution to keep the pH of the leachate at the initial value; the fermentation temperature is maintained at mesophilic 38℃, the residence time is 7 days, and the solid residue of acid-producing fermentation is dried to obtain biogas residue.

[0032] (3) Add biogas residue to raw water to carry out hydrothermal carbon reaction to obtain aqueous products and hydrothermal carbon;

[0033] Weigh 50g of the washed and dried biogas residue obtained in step (2), add 500mL of water (solid-liquid ratio of 50:500), mix evenly and put into a high-pressure reactor, heat to 210℃, react for 4h after heating, collect the solid-liquid mixture and separate it into aqueous product and solid hydrothermal carbon.

[0034] Specifically, after the reaction is complete, the inner liner of the reactor is removed, cooled to room temperature using a water bath, the exhaust valve is opened, and after no more gas is released from the reactor, the inner liner of the reactor is opened to collect the solid-liquid mixture; it is then placed in a Buchner funnel for filtration and separation; the aqueous phase product is hydrothermal carbonization wastewater (HTCWW), and the solid phase is hydrothermal carbon.

[0035] Experiment 2:

[0036] The difference between Experiment 2 and Experiment 1 is that 150g of the solid residue from the acid-producing fermentation in step (2) of Experiment 1 (containing 33.1% solids) was taken without any treatment and 400mL of water was added (the solid-liquid ratio after mixing was also 50:500) as the raw material for the hydrothermal carbon reaction; the other operation steps were the same as in Experiment 1.

[0037] The solids obtained from Experiments 1 and 2 were dried, weighed, and fully characterized. The yields of hydrothermal carbon in Experiments 1 and 2 were 58.4% and 56.1%, respectively. Analysis showed that their calorific values ​​were 17.2 MJ / kg and 17.9 MJ / kg, respectively, and their specific surface areas were 34.8 m² and 34.8 m², respectively. 2 / g and 39.7m2 / g. It can be seen that the hydrothermal carbon yield of Experiment 2 is lower than that of Experiment 1. This is mainly because the residual organic acid liquid in the solid residue of acid-producing fermentation can act as an acidic catalyst to further degrade the substrate. It also shows that solid residue containing organic acid is more conducive to increasing calorific value and specific surface area during hydrothermal carbonization.

[0038] Experiment 3:

[0039] The difference between Experiment 3 and Experiment 1 is that: instead of using biogas residue as the raw material for preparing hydrothermal char, silage straw is directly mixed with water as the raw material for the hydrothermal char reaction to produce aqueous products and hydrothermal char; the preparation steps are the same as in Experiment 1.

[0040] The results showed that the hydrothermal carbon yield was 53.3%, and the specific surface area was 26.4 m². 2 / g. Compared with Experiments 1 and 2, the yield and specific surface area of ​​hydrothermal char decreased. This is mainly because, in Experiments 1 and 2, after acid-producing fermentation of silage straw, the structural changes of lignocellulose after microbial degradation, the easy degradation characteristics of hemicellulose, and the degradability of cellulose led to the destruction of the inter-encapsulated structure of lignin, hemicellulose, and cellulose in the straw. During fermentation, pores can be formed on the basis of the original skeleton, which is conducive to the formation of pores in the hydrothermal carbonization process and contributes to the increase in specific surface area. Therefore, using biogas residue can produce hydrothermal char with better performance and improve the effect of subsequent fermentation using hydrothermal char as raw material.

[0041] Comparison of anaerobic fermentation effects of different raw materials:

[0042] Experiment 4:

[0043] (1) Following the steps in Experiment 1, hydrothermal carbonization wastewater (HTCWW) was obtained, and its COD concentration was measured to be 22870 mg / L, with NH4+ concentration of... + The -N concentration is 664.2 mg / L, which has the potential to produce methane through anaerobic fermentation.

[0044] (2) Measure different volumes of HTCWW to prepare raw materials with different initial organic concentrations and carry out anaerobic fermentation;

[0045] Specifically, 48.7g of anaerobic granular sludge was inoculated into a 500mL perforated blue-capped bottle. Different volumes of HTCWW were measured and placed into the blue-capped bottles (effective working volume was calculated as 400mL) to achieve initial organic concentrations of 2, 4, 6, 8, 10, and 12g COD / L, respectively. The pH of the fermentation broth was adjusted to 7.0 with 6mol / L NaOH solution. The top space of the reaction bottle was purged with nitrogen for 3 minutes and then sealed. The bottle was placed in a 38℃ water bath and shaken every 3 hours for 30 days. Each experiment was repeated under each condition.

[0046] Gases were collected daily from different blue-capped bottles to measure biogas volume and methane and carbon dioxide content, monitor the pH of fermentation broth, and sample and analyze VFAs, ammonia nitrogen, and COD concentrations. After fermentation, sludge samples were taken for analysis of microbial community structure and diversity, as well as determination of extracellular polymeric substances (EPS).

[0047] Experiment 5:

[0048] (1) Following step (1) of Experiment 1, hydrothermal carbonization wastewater (HTCWW) was obtained, with a COD concentration of 22870 mg / L and NH4+ concentration of 100 mg / L. + The -N concentration was the same as that of the hydrothermal carbonization wastewater used in Experiment 4.

[0049] (2) Anaerobic fermentation was carried out according to step (2) of Experiment 4, except that hydrothermal carbon obtained in Experiment 1 was added to each HTCWW anaerobic fermentation system.

[0050] Specifically, hydrothermal charcoal, after being washed and dried, is added to the entire HTCWW anaerobic fermentation system at a concentration of 500 mg / L.

[0051] The results showed that in Experiment 4, when the initial organic loading was 2 g COD / L, the methane yield was 142.5 mL CH4 / g COD. 去除 With an initial organic loading of 4 g COD / L, the methane yield was 183.8 mL CH4 / g COD. 去除 With an initial organic loading of 6 g COD / L, the methane yield was 269.8 mL CH4 / g COD. 去除 With an initial organic loading of 8 g COD / L, the methane yield was 275.9 mL CH4 / g COD. 去除 With an initial organic loading of 10 g COD / L, the methane yield was 118.4 mL CH4 / g COD. 去除 With an initial organic loading of 12 g COD / L, the methane yield was 42.4 mL CH4 / g COD. 去除 As shown in Table 1.

[0052] EPS monitoring revealed that when the load exceeded 8 g COD / L, the types of extracellular polymers and fluorescence intensity decreased. Combined with microbial community structure analysis, bacterial and archaeal diversity decreased. This indicates that under high load, the characteristic pollutants in the wastewater have a more significant toxic effect on microorganisms and have a greater impact on the fermentation and gas production process.

[0053] In Experiment 5, the addition of hydrothermal char reduced the toxicity to microorganisms. Compared with Experiment 4, when the initial organic load was 2 g COD / L, the methane yield was 187.5 mL CH4 / g COD. 去除 With an initial organic loading of 4 g COD / L, the methane yield was 219.8 mL CH4 / g COD. 去除 With an initial organic loading of 6 g COD / L, the methane yield was 290.8 mL CH4 / g COD. 去除 With an initial organic loading of 8 g COD / L, the methane yield was 299.9 mL CH4 / g COD. 去除 With an initial organic loading of 10 g COD / L, the methane yield was 229.7 mL CH4 / g COD. 去除 As shown in Table 1.

[0054] Table 1

[0055]

[0056]

[0057] In Experiment 5, when the initial organic load reached the inhibitory concentration threshold of 10 g COD / L, the methane yield was 229.7 mL CH4 / g COD. 去除 Under inhibitory loading conditions, the methane yield increased by 94% compared to Experiment 4. This is because hydrothermal carbon can reduce the toxicity of microorganisms by adsorbing characteristic pollutants. It can act as an adsorbent material to improve the tolerance of microorganisms to characteristic pollutants in wastewater and the adsorption effect on recalcitrant organic matter by immobilizing microorganisms. It can also act as an electron transport carrier to improve the electron transport efficiency of the redox reaction process and promote the effective conversion of organic acids to methane.

[0058] Comparison of the technical effects of using the supernatant from anaerobic fermentation in hydrothermal carbonization reaction:

[0059] Experiment Six

[0060] (1) Follow the steps (1) and (2) of Experiment 4. After the anaerobic fermentation is completed, centrifuge the material in the blue-capped bottle and collect the supernatant.

[0061] (2) The supernatant collected in step (1) completely replaces the raw water in step (3) of Experiment 1. After mixing with the biogas residue, hydrothermal carbon reaction is carried out, and the yield change of hydrothermal carbon is evaluated.

[0062] The results showed that the hydrothermal carbon yield was 61.1%, an increase of approximately 2.7% compared to Experiment 1. This was the highest yield among experiments aimed at preparing hydrothermal carbon. This is because after anaerobic fermentation, a certain amount of recalcitrant substances, such as nitrogen-containing heterocyclic compounds of pyridine and phenolic substances, remained in the supernatant of the hydrothermal carbonization wastewater. These recalcitrant substances participated in the condensation reaction during the carbonization process, contributing to the increase in product quality and further improving the hydrothermal carbon yield.

[0063] The technical benefits of reusing the solid residues from the anaerobic fermentation of hydrothermal carbonization wastewater for HTCWW treatment:

[0064] Experiment 7

[0065] (1) Follow the steps (1) and (2) of Experiment 4. After the anaerobic fermentation is completed, centrifuge the material in the blue-capped bottle and collect the solid fermentation residue.

[0066] (2) The solid residue collected in step (1) was used as inoculum to completely replace the anaerobic granular sludge in step (2) of experiment four. After mixing with hydrothermal carbonization wastewater, anaerobic fermentation was carried out. The initial organic load was controlled at 8 g COD / L, and its gas production effect was evaluated.

[0067] The results showed that under this loading condition, the methane yield could reach 283.6 mL CH4 / g COD. 去除 This indicates that anaerobic granular sludge, after acclimation, can improve its utilization and tolerance of substrates, and enrich key functional microbial communities, which can improve methanogenesis when used as inoculum again.

[0068] Experiment 8

[0069] (1) Follow the steps (1) and (2) of Experiment 4. After the anaerobic fermentation is completed, centrifuge the material in the blue-capped bottle and collect the solid fermentation residue.

[0070] (2) The solid residue collected in step (1) was used as the inoculum to completely replace the anaerobic granular sludge in step (2) of Experiment 4. It was mixed with hydrothermal carbonization wastewater and the hydrothermal carbon was added to the entire HTCWW anaerobic fermentation system at a concentration of 500 mg / L after washing and drying, as described in Experiment 5. Anaerobic fermentation was then carried out with the initial organic load controlled at 8 g COD / L, and the gas production effect was evaluated.

[0071] The results showed that under this loading condition, the methane yield could reach 288.2 mL CH4 / g COD.去除 This indicates that the beneficial combination of all products and by-products in the entire co-production process plays an important role in the closed-loop treatment of biogas residue.

[0072] Experiments 1, 2, and 3 show that the yield of hydrothermal char produced using biogas residue is higher than that produced using silage straw. Experiments 4, 5, 7, and 8 show that the methane yield is higher when hydrothermal char is mixed with wastewater for anaerobic fermentation compared to using only hydrothermal char treatment wastewater. Adding the solid residue from anaerobic fermentation as an inoculum for acclimatization further improves the methane yield compared to the initial inoculum. Experiments 1 and 6 show that recycling the supernatant from anaerobic fermentation for hydrothermal char production yields an even higher hydrothermal char yield. Therefore, the closed-loop biogas residue treatment and utilization method based on gas-char co-production of the present invention can achieve high hydrothermal char yield and methane production rate.

[0073] Therefore, this invention uses hydrothermal carbonization technology to treat the solid residues from the acid-producing stage of the two-phase straw process to obtain hydrothermal carbon. The effective components of the aqueous phase byproducts (short-chain organic acids and monosaccharides such as glucose and xylose) are then anaerobically converted to generate methane. The fermented wastewater is reused as a reaction medium for hydrothermal carbonization of the biogas residue, while the hydrothermal carbon is used as a biological promoter in combination with the anaerobic fermentation of wastewater, thus realizing a closed-loop recycling of the entire biogas residue treatment process.

[0074] Compared to using biogas residue to make organic fertilizer, the advantages of this invention are: hydrothermal carbonization is suitable for processing materials with high moisture content (80-90%). If biogas residue with high moisture content is used for composting, auxiliary materials need to be added to adjust the moisture content to 60-65%. Moreover, from the perspective of high-value utilization, the price of hydrothermal carbon is much higher than the current market price of organic fertilizer, and it has a better industrial prospect.

[0075] The above description is merely a preferred embodiment of the present invention and is not intended to limit the 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 closed-loop treatment and utilization method for biogas residue based on gas-coke cogeneration, characterized in that, Includes the following steps: S1. The biogas residue is mixed with the raw water and subjected to hydrothermal carbonization technology. The solid-liquid mass ratio of biogas residue to raw water is 50:500, the reaction temperature is 210℃, and the reaction time is 4h to obtain hydrothermal carbonization wastewater and hydrothermal carbon. S2. Mix hydrothermal carbonization wastewater with hydrothermal carbon and carry out anaerobic fermentation to obtain biogas and fermentation products; S3. Centrifuge the fermentation material to obtain the supernatant. Recycle the supernatant into S1. Use the solid fermentation residue obtained by centrifugation as inoculum for domestication into S2. Among them, the biogas residue in S1 is obtained by acid-producing fermentation.

2. The closed-loop treatment and utilization method for biogas residue based on gas-coal cogeneration as described in claim 1, characterized in that, The method of acid-producing fermentation is as follows: silage straw and / or dry straw are mixed with anaerobic granular sludge. In the initial stage of the reaction of the mixture, the pH is adjusted to 8, and acid production begins through percolation. The fermentation temperature is maintained at a mesophilic temperature of 38°C, and the retention time is 7 days. The solid residue of acid-producing fermentation is biogas residue.

3. The closed-loop treatment and utilization method for biogas residue based on gas-coal cogeneration as described in claim 2, characterized in that, The VS ratio of silage straw and / or dry straw to anaerobic granular sludge is 4:

1. The pH of the leachate is controlled every 4 hours throughout the process, and the pH of the leachate is always controlled at the initial value.

4. The closed-loop treatment and utilization method for biogas residue based on gas-coal cogeneration as described in claim 1, characterized in that, In S2, anaerobic granular sludge is added as inoculum, and hydrothermal carbonization wastewater is mixed with hydrothermal carbon and fermented at 38°C to collect biogas and fermentation products.

5. The closed-loop treatment and utilization method for biogas residue based on gas-coke cogeneration as described in claim 4, characterized in that, The hydrothermal carbonization wastewater was mixed with water to achieve a COD concentration of 8 g COD / L.

6. The closed-loop treatment and utilization method for biogas residue based on gas-coke cogeneration as described in claim 1, characterized in that, In S2, Buchner funnel filtration separation is used.

7. The closed-loop treatment and utilization method for biogas residue based on gas-coke cogeneration as described in claim 1, characterized in that, In S3, the supernatant completely replaces the raw water in S1.

8. The closed-loop treatment and utilization method for biogas residue based on gas-coke cogeneration as described in claim 1, characterized in that, In S2, the hydrothermal carbon is added at a ratio of 500 mg / L into the anaerobic fermentation system for hydrothermal carbonization wastewater.

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