Nitrogen and iron doped hydrothermal carbon as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of organic solid waste treatment, and particularly discloses nitrogen and iron doped hydrothermal carbon and a preparation method and application thereof.The preparation method includes the following steps that a biogas slurry and biogas residue mixture obtained after anaerobic fermentation of excrement, fruit tree residues and high-iron sludge are evenly mixed according to the solid-to-liquid ratio of 1: 6-1: 10, hydrothermal carbonization is conducted, and the mass ratio of the fruit tree residues to the high-iron sludge is 1: 4-1: 6; the reaction is closed in the hydrothermal carbonization process, nitrogen is introduced, the hydrothermal carbonization temperature is 180-260 DEG C, and the hydrothermal carbonization time is 1-3 h; and carrying out solid-liquid separation on the hydrothermal product to obtain a solid product and a hydrothermal waste liquid, and drying the solid product to obtain the dry nitrogen and iron doped hydrothermal carbon. Aiming at the problem that the biogas slurry is difficult to return to the field, the biogas residue and biogas slurry mixed liquid is used as a raw material for hydrothermal carbonization, the nitrogen-iron doped hydrothermal carbon is prepared through hydrothermal carbonization reaction by utilizing the high-nitrogen characteristic of the biogas residue and biogas slurry mixed liquid and coupling the high-iron characteristic of the high-iron sludge, and compared with common hydrothermal carbon, the nitrogen-iron doped hydrothermal carbon has a better anaerobic fermentation strengthening effect.

Description

Technical Field

[0001] The invention belongs to the technical field of high-nitrogen organic solid waste treatment, and specifically relates to nitrogen-iron doped hydrothermal charcoal and a preparation method and application thereof. Background Art

[0002] The statements herein merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] High-nitrogen organic wastes include municipal sludge, kitchen waste, livestock and poultry manure, slaughter sludge, etc. Unlike high C / N ratio raw materials such as straw, the use of traditional methods to treat the above-mentioned high-nitrogen organic wastes has problems such as significant inhibition effect, high nitrogen loss ratio, low energy conversion rate, and difficulty in utilizing liquid products after disposal. At present, the main energy and resource technology for high-nitrogen organic wastes is anaerobic fermentation technology, but in the anaerobic fermentation system with high-nitrogen organic wastes as the main raw material, the ammonia nitrogen concentration can reach 5000-6000 mg / L. Under the high ammonia nitrogen inhibition environment, the coordination between multiple metabolic pathways will be destroyed, especially the hydrogenophilic methanogenic pathway. Under the inhibition, the population abundance and metabolic activity are reduced, which is easy to cause the accumulation of volatile fatty acids, further inhibiting the acidophilic methanogenic process, thereby causing the instability of the entire anaerobic fermentation process. In addition, the return of anaerobic fermentation slurry to the field is greatly restricted by agricultural planting patterns, seasons, farmland carrying capacity, and transportation costs. Most of it accumulates in the biogas plant and cannot be consumed, which has become an important factor restricting the rapid development of biogas projects.

[0004] Hydrothermal carbonization technology has many advantages, such as no need for pre-drying of raw materials, autogenous pressure, and water-promoted reactions. As a solid product produced by hydrothermal carbonization reaction, hydrothermal carbon has a certain specific surface area and pore structure, and contains rich oxygen-containing functional groups. Adding an appropriate amount of hydrothermal carbon to the anaerobic fermentation system can shorten the start-up period of anaerobic fermentation, increase the methane content in anaerobic fermentation biogas, and enhance the tolerance of the fermentation system to adverse fermentation environments such as acid and ammonia inhibition, which has a more obvious effect of strengthening anaerobic fermentation and methane production. However, the hydrothermal carbonization process produces a large amount of waste liquid. How to safely and effectively treat and dispose of it, and how to recycle and reuse the effective components in the waste liquid are also urgent problems to be solved. Summary of the invention

[0005] In view of the deficiencies in the prior art, the object of the present invention is to provide a nitrogen-iron doped hydrothermal carbon and a preparation method and application thereof.

[0006] In order to achieve the above object, the present invention is implemented through the following technical solutions:

[0007] In a first aspect, the present invention provides a method for preparing nitrogen-iron doped hydrothermal carbon, comprising the following steps: mixing a mixture of biogas slurry and biogas residue after anaerobic fermentation of feces, fruit wood residue and high-iron sludge at a solid-liquid ratio of 1:6-1:10, and performing hydrothermal carbonization, wherein the mass ratio of fruit wood residue to high-iron sludge is 1:4-1:6;

[0008] During the hydrothermal carbonization process, the reaction is closed and nitrogen is introduced. The temperature of the hydrothermal carbonization is 180-260°C and the time of the hydrothermal carbonization is 1-3h.

[0009] The hydrothermal product is separated into solid and liquid to obtain a solid product and hydrothermal waste liquid. After the solid product is dried, dry nitrogen-iron doped hydrothermal carbon is obtained.

[0010] In some embodiments, the feces are duck manure, chicken manure, pig manure, etc., preferably duck manure.

[0011] In some embodiments, the moisture content of wood residue is 5%-10%; the moisture content of high iron sludge is 65%-75%, where % is mass percentage.

[0012] Preferably, the iron content in the high-iron sludge is 5-20%, where % is mass percentage.

[0013] In some embodiments, the hydrothermal carbonization process is continuously stirred.

[0014] In some embodiments, the temperature of the hydrothermal carbonization is 200-260°C.

[0015] Preferably, the hydrothermal carbonization time is 1.5-2.5 h.

[0016] In a second aspect, the present invention provides nitrogen-iron doped hydrothermal carbon, which is prepared by the preparation method. In the nitrogen-iron doped hydrothermal carbon, the mass percentage of iron is higher than 10%, and the mass percentage of nitrogen is higher than 4%.

[0017] In a third aspect, the present invention provides the use of the nitrogen-iron doped hydrothermal carbon in catalyzing anaerobic fermentation of high nitrogen-containing organic waste to increase methane production.

[0018] In a fourth aspect, the present invention provides a method for anaerobic fermentation of high-nitrogen organic waste, comprising the following steps:

[0019] Mix high nitrogen organic waste, anaerobic fermentation bacteria, nitrogen and iron doped hydrothermal charcoal and / or hydrothermal waste liquid in proportion, and perform anaerobically fermentation at 35-40°C for 30-40 days;

[0020] The mass fraction of nitrogen-iron doped hydrothermal charcoal in high nitrogen-containing organic waste is 1%-3%;

[0021] The mass fraction of hydrothermal waste liquid in high nitrogen-containing organic waste is 20%-100%.

[0022] In some embodiments, the high nitrogen organic waste is livestock and poultry manure, slaughter sludge, municipal sludge or food waste.

[0023] Preferably, the high nitrogen content organic waste is duck manure.

[0024] The beneficial effects achieved by one or more embodiments of the present invention are as follows:

[0025] In order to solve the problem of difficulty in returning biogas slurry to the fields, the present invention uses the mixture of biogas residue and biogas slurry as the raw material for hydrothermal carbonization, utilizes its high nitrogen property, and couples it with the high iron property of high-iron sludge to prepare nitrogen-iron doped hydrothermal carbonization reaction. Compared with ordinary hydrothermal carbon, the enhanced effect on anaerobic fermentation is better.

[0026] In order to address the problems of operational instability and inhibition of intermediate and end products during anaerobic fermentation of high-nitrogen organic waste, nitrogen-iron doped hydrothermal carbon is added to the anaerobic fermentation system to strengthen and stabilize the fermentation process. In order to address the problem of difficult treatment of hydrothermal waste liquid, it is returned to the anaerobic fermentation system to further recover the nutrients in it. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0028] Figure 1 is a comparison chart of methane daily production of various embodiments of the present invention and comparative examples;

[0029] Figure 2 is a comparison chart of the cumulative methane production per gram of volatile organic matter in various embodiments of the present invention and comparative examples;

[0030] Figure 3 It is a process flow chart of an embodiment of the present invention. DETAILED DESCRIPTION

[0031] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0032] The present invention will be further described below in conjunction with the embodiments.

[0033] Example 1

[0034] Hydrothermal carbonization test: The mixture of sludge and residue after anaerobic fermentation of duck manure, fruit wood residue and high-iron sludge were used as hydrothermal carbonization raw materials, wherein the moisture content of the sludge and residue mixture was 95%, the moisture content of the fruit wood residue was 6%, and the moisture content of the high-iron sludge (the iron content of the high-iron sludge was 10%) was 70%. The solid-liquid ratio was controlled to be 1:8, and the solid content ratio of the fruit wood residue, sludge and residue mixture and high-iron sludge was 19:29:30. The reaction was placed in a reactor for hydrothermal carbonization reaction, during which nitrogen was passed through a closed system and stirred continuously. The stirring rate was 400 rpm, the heating rate was 5°C / min, the target temperature was 230°C, the holding time was 2h, and then naturally cooled. The hydrothermal product was filtered and dried to obtain dry nitrogen-iron-doped hydrothermal carbon and hydrothermal waste liquid.

[0035] Anaerobic fermentation test: Duck manure was used as the fermentation raw material, with 22g of duck manure, 22% of total solid content, 85% of volatile organic matter in the total solids, and nitrogen and iron-doped hydrothermal charcoal and hydrothermal waste liquid were added. The mass ratio of hydrothermal charcoal to duck manure was 2%, and the mass ratio of hydrothermal waste liquid to duck manure was 60%. The fermentation temperature was 37°C, and the shaking table culture was used. The culture system was a 500ml anaerobic bottle, and the culture period was 32 days.

[0036] In this hydrothermal carbonization test, the total weight of raw materials is 700g, including 20g of fruit wood residue, 580g of biogas slurry and 100g of high-iron sludge; the total weight of the product dry nitrogen-iron doped hydrothermal carbon is 42g, and the hydrothermal carbon yield is 6%.

[0037] This anaerobic fermentation test was numbered as Group H1. The drainage gas extraction method was used to determine the methane production during the anaerobic fermentation process. The daily biogas production was measured once every 4 days. The biogas production is shown in Table 1.

[0038] Table 1 Daily methane production of H1 group (mL)

[0039]

[0040] Example 2

[0041] Hydrothermal carbonization test: The mixture of sludge and residue after anaerobic fermentation of duck manure, fruit wood residue and high-iron sludge were used as hydrothermal carbonization raw materials, wherein the moisture content of the sludge and residue mixture was 95%, the moisture content of fruit wood residue was 6%, and the moisture content of high-iron sludge (the iron content of high-iron sludge was 10%) was 70%. The solid-liquid ratio was controlled to be 1:8, and the solid content ratio of fruit wood residue, sludge and high-iron sludge was 19:29:30. The reaction kettle was placed for hydrothermal carbonization reaction, during which nitrogen was passed through the closed system and stirred continuously. The stirring rate was 400 rpm, the heating rate was 5°C / min, the target temperature was 230°C, the holding time was 2h, and then naturally cooled. The hydrothermal product was filtered and dried to obtain dry nitrogen-iron doped hydrothermal carbon and hydrothermal waste liquid.

[0042] Anaerobic fermentation test: Duck manure was used as the fermentation raw material, with 22g of duck manure, a total solid content of 22%, and volatile organic matter accounting for 80% of the total solids. Nitrogen and iron-doped hydrothermal charcoal was added, and the mass ratio of hydrothermal charcoal to duck manure was 2%. No hydrothermal waste liquid was added, the fermentation temperature was 37°C, and shaking culture was adopted. The culture system was a 500ml anaerobic bottle, and the culture period was 32 days.

[0043] In this hydrothermal carbonization test, the total weight of the raw materials is 700 g, and the composition is the same as in Example 1. The total weight of the product dry nitrogen-iron doped hydrothermal carbon is 42 g, and the hydrothermal carbon yield is 6%.

[0044] This anaerobic fermentation test was numbered as Group H2. The drainage gas extraction method was used to determine the methane production during the anaerobic fermentation process. The daily biogas production was obtained once every 4 days. The biogas production is shown in Table 2.

[0045] Table 2 Daily methane production of H2 group (mL)

[0046]

[0047] Example 3

[0048] Hydrothermal carbonization test: The mixture of sludge and residue after anaerobic fermentation of duck manure, fruit wood residue and high-iron sludge were used as hydrothermal carbonization raw materials, wherein the moisture content of the sludge and residue mixture was 95%, the moisture content of fruit wood residue was 6%, and the moisture content of high-iron sludge (the iron content of high-iron sludge was 10%) was 70%. The solid-liquid ratio was controlled to be 1:8, and the solid content ratio of fruit wood residue, sludge and high-iron sludge was 19:29:30. The reaction kettle was placed for hydrothermal carbonization reaction, during which nitrogen was passed through the closed system and stirred continuously. The stirring rate was 400 rpm, the heating rate was 5°C / min, the target temperature was 230°C, the holding time was 2h, and then naturally cooled. The hydrothermal product was filtered and dried to obtain dry nitrogen-iron doped hydrothermal carbon and hydrothermal waste liquid.

[0049] Anaerobic fermentation test: Duck manure was used as the fermentation raw material, with 22g of duck manure, 30% total solid content, 90% volatile organic matter in the total solids, and hydrothermal waste liquid was added, with a mass ratio of hydrothermal waste liquid to duck manure of 50%. No nitrogen-iron-doped hydrothermal charcoal was added, the fermentation temperature was 37°C, and shaking culture was adopted. The culture system was a 500ml anaerobic bottle, and the culture period was 32 days.

[0050] In this hydrothermal carbonization test, the total weight of the raw materials is 700 g, and the composition is the same as in Example 1. The total weight of the product dry nitrogen-iron doped hydrothermal carbon is 42 g, and the hydrothermal carbon yield is 6%.

[0051] This anaerobic fermentation test was numbered as Group H3. The drainage gas extraction method was used to determine the methane production during the anaerobic fermentation process. The daily biogas production was measured once every 4 days. The biogas production is shown in Table 3.

[0052] Table 3 Daily methane production of H3 group (mL)

[0053]

[0054] Comparative Example 1

[0055] Hydrothermal carbonization test: Fruit wood residue was used as the hydrothermal carbonization raw material. The moisture content of the fruit wood residue was 6%. The solid-liquid ratio was controlled at 1:8 and placed in a reactor for hydrothermal carbonization reaction. During the reaction, nitrogen was passed through the reactor in a closed manner and stirred continuously. The stirring rate was 400 rpm, the heating rate was 5°C / min, the target temperature was 230°C, the holding time was 2h, and then naturally cooled. The hydrothermal product was filtered and dried to obtain hydrothermal charcoal.

[0056] Anaerobic fermentation test: Duck manure was used as the fermentation raw material, with 22g of duck manure, 22% total solid content, 85% volatile organic matter in the total solids, fruit wood hydrocharcoal was added, the mass ratio of hydrocharcoal to duck manure was 2%, the fermentation temperature was 37°C, shaking table culture was used, the culture system was 500ml anaerobic bottle, and the culture period was 32 days.

[0057] In this hydrothermal carbonization test, the total weight of raw materials is 700g, including 82g of fruit wood residue and 618g of water. The total weight of the product dry hydrothermal carbon is 35g, and the hydrothermal carbon yield is 5%.

[0058] This anaerobic fermentation test was numbered as Group C1. The drainage gas extraction method was used to determine the methane production during the anaerobic fermentation process. The daily biogas production was obtained once every 4 days. The biogas production is shown in Table 4.

[0059] Table 4 Daily methane production of group C1 (mL)

[0060]

[0061] Comparative Example 2

[0062] The difference from Example 1 is that when preparing the hydrothermal charcoal, the mixture of biogas slurry and biogas residue after anaerobic fermentation of duck manure is omitted, and the rest is the same as Example 1.

[0063] This anaerobic fermentation test was numbered as Group C2 and lasted for 32 days. The methane production during the anaerobic fermentation process was determined by the drainage gas extraction method. The daily biogas production was obtained once every 4 days. The biogas production is shown in Table 5.

[0064] Table 5 Daily methane production of C2 group (mL)

[0065]

[0066] Comparative Example 3

[0067] The difference from Example 1 is that when preparing hydrothermal carbon, high iron sludge is omitted, and the rest is the same as Example 1.

[0068] This anaerobic fermentation test was numbered as Group C3 and lasted for 32 days. The methane production during the anaerobic fermentation process was determined by the drainage gas extraction method. The daily biogas production was obtained once every 4 days. The biogas production is shown in Table 6.

[0069] Table 6 Daily methane production of C3 group (mL)

[0070]

[0071] Comparative Example 4

[0072] Anaerobic fermentation test: duck manure and inoculum were used as fermentation raw materials, the inoculum was 220 mL, the duck manure was 22 g, the total solid content of duck manure was 22%, and the volatile organic matter accounted for 85% of the total solids. No hydrothermal charcoal and hydrothermal waste liquid were added. The fermentation temperature was 37°C, and the shaking table culture was used. The culture system was a 500 ml anaerobic bottle, and the culture period was 32 days.

[0073] This anaerobic fermentation test was numbered as Group C4 and lasted for 32 days. The methane production during the anaerobic fermentation process was determined by the drainage gas extraction method. The daily biogas production was obtained once every 4 days. The biogas production is shown in Table 7.

[0074] Table 7 Daily methane production of C4 group (mL)

[0075]

[0076] The elemental analysis of nitrogen-iron doped hydrothermal charcoal and fruit wood hydrothermal charcoal is shown in Table 8, where % is the mass percentage.

[0077] Table 8 Elemental analysis of nitrogen-iron doped hydrothermal charcoal and fruit wood hydrothermal charcoal

[0078] N(％) C(％) H(％) Fe(%) Other elements (%) Nitrogen-iron doped hydrothermal carbon 6.1 13.18 2.02 20.5 58.2 Fruit wood hydrothermal charcoal 2.05 12.45 2.58 0.06 82.86

[0079] The specific surface area and industrial analysis of nitrogen-iron doped hydrothermal charcoal and fruit wood hydrothermal charcoal are shown in Table 9, where % is the mass percentage.

[0080] Table 9 Composition and specific surface area of ​​nitrogen-iron doped hydrothermal charcoal and fruit wood hydrothermal charcoal

[0081]

[0082] From Table 8, the nitrogen element accounts for 7.1% and the iron element accounts for 8.08% in the nitrogen-iron doped hydrothermal charcoal, which are significantly higher than those of fruit wood hydrothermal charcoal and have the characteristics of high nitrogen and high iron.

[0083] From Table 9, the volatile matter of nitrogen-iron doped hydrothermal charcoal is slightly higher than that of fruit wood hydrothermal charcoal, and the ash content is slightly lower than that of fruit wood hydrothermal charcoal. The moisture content, fixed carbon and specific surface area are relatively close.

[0084] from Figure 1 It can be seen that the daily methane production trends of all experimental groups were similar, reaching the peak of gas production around the 12th day. After reaching the peak, the gas production gradually decreased, tended to be stable on the 28th day, and basically stopped on the 32nd day.

[0085] The methane production of the group with added hydrochar increased rapidly in 4-8 days, and the daily methane production was higher than that of the C4 group without added hydrochar. The daily methane production of the H2 group with added nitrogen-iron doped hydrochar was higher than that of the C1, C2, and C3 groups with added other types of hydrochar.

[0086] The methane production in the H1 group was the highest at 196.04 mL on days 4-8, while that in the C4 group was the lowest at 117.40 mL. The H1 group increased by 66.98% compared with the C4 group.

[0087] The methane production in the H1 group was the highest at 277.32 mL on days 8-12, while that in the C4 group was the lowest at 230.25 mL. The H1 group increased by 20.44% compared with the C4 group.

[0088] Table 10 Cumulative methane production per gram of volatile organic matter in the test group (mL / gVS)

[0089]

[0090] After deducting the methane production of the inoculum, the cumulative methane production per gram of volatile organic matter in duck feces of each experimental group was obtained. As can be seen from Table 10, the cumulative methane production per gram of volatile organic matter in the H1 group was the highest at 206.572 mL / g VS, and the C4 group was the lowest at 146.723 mL / g VS, which was 40.79% higher than that in the C4 group.

[0091] from Figure 2 It can be seen that the cumulative methane production per gram of volatile organic matter in the experimental groups is ranked from high to low as follows: H1>H2>H3>C2>C3>C1>C4.

[0092] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing nitrogen-iron doped hydrothermal carbon, characterized in that: The method comprises the following steps: mixing the biogas slurry and biogas residue mixture after anaerobic fermentation of feces, fruit wood residue and high-iron sludge at a solid-liquid ratio of 1:6-1:10, and performing hydrothermal carbonization, wherein the mass ratio of the fruit wood residue to the high-iron sludge is 1:4-1:6; During the hydrothermal carbonization process, the reaction is closed and nitrogen is introduced. The temperature of the hydrothermal carbonization is 180-260°C and the time of the hydrothermal carbonization is 1-3h. The hydrothermal product is separated into solid and liquid to obtain a solid product and hydrothermal waste liquid. After the solid product is dried, dry nitrogen-iron doped hydrothermal carbon is obtained.

2. The method for preparing nitrogen-iron doped hydrothermal carbon according to claim 1, characterized in that: The excrement is duck excrement, chicken excrement, pig excrement and the like.

3. The method for preparing nitrogen-iron doped hydrothermal carbon according to claim 1, characterized in that: The moisture content of fruit wood residue is 5%-10%; the moisture content of high iron sludge is 65%-75%; Preferably, the iron content in the high-iron sludge is 5-20%, where % is mass percentage.

4. The method for preparing nitrogen-iron doped hydrothermal carbon according to claim 1, characterized in that: The hydrothermal carbonization process was stirred continuously.

5. The method for preparing nitrogen-iron doped hydrothermal carbon according to claim 1, characterized in that: The temperature of hydrothermal carbonization is 200-260℃; Preferably, the hydrothermal carbonization time is 1.5-2.5 h.

6. A nitrogen-iron doped hydrothermal carbon, characterized in that: Prepared by the preparation method according to any one of claims 1 to 5, in the nitrogen-iron doped hydrothermal carbon, the mass percentage of iron is higher than 10%, and the mass percentage of nitrogen is higher than 4%.

7. Use of the nitrogen-iron doped hydrothermal carbon as described in claim 6 in catalyzing anaerobic fermentation of high nitrogen-containing organic waste to increase methane production.

8. A method for anaerobic fermentation of high nitrogen organic waste, characterized in that: The steps include: Mixing high nitrogen organic waste, anaerobic fermentation inoculum, and the nitrogen-iron doped hydrothermal charcoal of claim 6 and / or the hydrothermal waste liquid of claim 1 in proportion, and performing anaerobically fermentation at 35-40° C. for 30-40 days; The mass fraction of nitrogen-iron doped hydrothermal charcoal in high nitrogen-containing organic waste is 1%-3%; The mass fraction of hydrothermal waste liquid in high nitrogen-containing organic waste is 20%-100%.

9. The method for anaerobic fermentation of high nitrogen-containing organic waste according to claim 8, characterized in that: The high nitrogen content organic waste is livestock and poultry manure, slaughter sludge, municipal sludge or restaurant kitchen waste.

10. The method for anaerobic fermentation of high nitrogen content organic waste according to claim 9, characterized in that: The high nitrogen content organic waste is livestock and poultry manure, municipal sludge, slaughter sludge, restaurant kitchen waste, etc., preferably duck manure.

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