Iron modified waste residue biochar as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of organic solid waste resource utilization, and particularly relates to iron modified waste residue biochar as well as a preparation method and application thereof. The preparation method comprises the following steps: mixing lignin-rich waste residues with a specific ferric salt solution, obtaining a carbon precursor by virtue of an impregnation method, and promoting biomass pyrolysis to form a graphitized structure by virtue of pyrolysis calcination, so as to obtain the Fe-loaded modified waste residue biochar. The obtained iron-modified waste residue biochar is added into an anaerobic digestion system with organic waste as a substrate, the stability of the anaerobic system can be enhanced by means of the high adsorption and buffering capacity of the biochar, Fe loaded on the surface of the iron-modified waste residue biochar can serve as an electronic mediator, the activity of related enzymes in the anaerobic system is enhanced, and the anaerobic digestion efficiency is improved. Meanwhile, the electrochemical performance of the biochar is enhanced, microelements required by growth can be provided for microorganisms, and the digestion efficiency of the system is improved, so that the total yield of methane subjected to anaerobic digestion is increased, and harmless treatment and resource utilization of organic wastes can be realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of organic solid waste resource utilization, and more specifically, relates to an iron-modified waste residue biochar and a preparation method and application thereof. Background Art

[0002] At present, the production technology of cellulosic ethanol, which mainly uses cellulose biomass such as agricultural and forestry waste and energy crops as raw materials, has become mature. However, the industry has encountered challenges in the treatment of waste generated at the end of the refining process, especially the harmless treatment of refining wastewater with high chemical oxygen demand (SCOD) and refining waste residue with high lignin content. The economic benefit issue has become a key bottleneck hindering the widespread application of cellulosic ethanol.

[0003] Anaerobic digestion technology, as an effective means of converting waste organic matter into clean energy, has shown great potential in reducing, harmlessly treating and recycling biomass waste in recent years, becoming a research focus in the field of environmental protection and having broad market application prospects. The high-concentration organic wastewater generated during the refining process of cellulosic ethanol is rich in methane production potential, but when used directly as a substrate for anaerobic digestion, it will face the problems of organic acid accumulation and limited methanogen activity, resulting in reduced digestion efficiency and reduced biogas methane production.

[0004] To solve this problem, biochar and other carriers are widely used to improve the performance of anaerobic digestion due to their large specific surface area, good adsorption and fixation capacity, and strong conductivity, including alleviating the inhibitory effect, promoting microbial enrichment, and enhancing the efficiency of direct interspecies electron transfer (DIET), thereby increasing methane production. There have been many cases reported on the application of biochar in enhanced anaerobic digestion, such as pigeon manure biochar for mixed anaerobic digestion of pig manure and rice straw, Spartina alterniflora biochar for enhanced anaerobic digestion of residual sludge containing polyacrylamide (PAM), and wood biochar for promoting dark fermentation of sludge to produce hydrogen.

[0005] In addition, by introducing iron salt modification, the electrochemical properties of the carrier can be further improved, creating an environment conducive to the growth of anaerobic microbial communities and promoting the generation of biogas methane. For example, Chinese patent application CN118207200A proposes a method for strengthening the co-digestion of cow dung and corn straw by iron-modified zeolite. This method uses FeCl3 / NZ iron-modified zeolite, which has the advantages of low pollution and simple operation, enhances the buffering capacity of the system, improves the activity of microorganisms and major enzymes, and significantly improves the methane production efficiency. However, when exogenous additives such as modified biochar are modified by adding iron elements or other substances, although they can bring a series of positive effects, such as optimizing pore structure, promoting organic matter degradation and improving microbial community structure, thereby improving the methane production efficiency of the anaerobic digestion system, they may also introduce some negative effects. These negative effects may be caused by impurities introduced during the modification process, incompatibility between the modifier and the properties of the biochar itself, or the inhibitory effect of modified biochar on anaerobic microorganisms under specific conditions. When these negative effects outweigh its positive effects, modified biochar may become a factor that inhibits the production of methane by anaerobic microorganisms.

[0006] Therefore, the current research focus is on finding an ideal modified biochar, which should be modified in a way that can fully utilize the advantages of biochar and effectively avoid or mitigate potential negative effects. When added to the anaerobic digestion system as an exogenous additive, this modified biochar should be able to significantly increase the methane production rate of the system, providing strong support for the optimization and upgrading of anaerobic digestion technology. Summary of the invention

[0007] The technical problem to be solved by the present invention is to overcome the defect and deficiency that the negative impact of the modified biochar in the above-mentioned prior art is greater than the positive impact, and instead becomes a factor that inhibits anaerobic microorganisms from producing methane, and to provide a method for preparing iron-modified waste residue biochar.

[0008] The purpose of the present invention is to provide an iron-modified waste residue biochar.

[0009] Another object of the present invention is to provide the use of the iron-modified waste residue biochar in anaerobic digestion.

[0010] Another object of the present invention is to provide a method for producing methane by utilizing organic waste.

[0011] The above-mentioned purpose of the present invention is achieved through the following technical solutions:

[0012] The present invention provides a method for preparing iron-modified waste residue biochar, comprising the following steps:

[0013] S1. The lignin-rich waste residue is fully impregnated in an iron salt solution and dried to obtain an iron-modified carbon precursor;

[0014] S2. The obtained iron-modified carbon precursor is heat-treated at 400-700° C. in a protective atmosphere, fully calcined, and post-treated to obtain iron-modified waste residue biochar;

[0015] Wherein, the cellulose content in the lignin-rich waste residue is ≥9%, and the lignin content is ≥50%;

[0016] The iron salt is selected from ferric citrate or its hydrate.

[0017] The present invention mixes lignin-rich waste residue with a specific iron salt solution, obtains a carbon precursor by an impregnation method, promotes biomass pyrolysis to form a graphitized structure through pyrolysis and calcination, improves the redox activity of biochar materials, enriches electron donors and acceptors to promote system electron transfer, and prepares iron-modified waste residue biochar. The obtained iron-modified waste residue biochar has a large specific surface area, and its porous structure can provide anaerobic system functional bacteria for attachment growth and inhibitors (such as organic acids, ammonia, etc.) adsorption, thereby promoting nutritional metabolism and enhancing the stability of the anaerobic system; at the same time, the Fe loaded on the surface of the iron-modified waste residue biochar can be used as an electron mediator, and the introduction of iron salts can enhance the activity of related enzymes in the anaerobic system, while enhancing the electrochemical properties of biochar, using biochar as a carrier to improve the direct interspecies electron transfer efficiency of microorganisms in the anaerobic system, promote the use of volatile fatty acids (Volatile Fatty Acids, VFAs) and H2 by methanogens, and adjust the pH of the stable system, thereby improving the stability of the anaerobic system and achieving efficient and stable bioenergy recovery. In addition, since ferric citrate contains abundant functional groups such as carboxyl and hydroxyl groups and iron elements, its loading on the surface of biochar can also improve the electrical adsorption performance of biochar. The combination of ferric citrate and waste residue biochar can not only give full play to the advantages of biochar, but also effectively avoid or reduce its potential negative effects, maximizing the combined advantages of iron elements and biochar. Therefore, the obtained modified biochar can improve the efficiency of anaerobic digestion. On the one hand, the addition of the iron-modified waste residue biochar reduces the inhibitory effect caused by the accumulation of VFAs and improves the stability and digestion efficiency of the anaerobic system; on the other hand, it promotes the generation of biogas methane in the anaerobic system, increases the substrate methane yield, and can achieve harmless treatment and resource utilization of organic waste.

[0018] Furthermore, the lignin-rich waste residue is cellulosic ethanol refining waste residue, which is mainly derived from the fermentation mash of the ethanol distillation tower and is composed of lignin components that cannot be fully utilized during the hydrolysis and fermentation process of cellulose biomass.

[0019] More preferably, the mass ratio of the iron salt to the lignin-rich waste residue is 1:(8-15).

[0020] Preferably, the heating rate of the heat treatment is 5-10°C / min.

[0021] Furthermore, the post-treatment includes cooling, washing and drying.

[0022] Furthermore, the washing is performed by filtering and washing with anhydrous ethanol and water for 3 to 5 times respectively.

[0023] Furthermore, the drying is carried out at 80-105°C.

[0024] Specifically, the post-treatment is to cool the product obtained after the heat treatment to room temperature, filter and wash it with anhydrous ethanol and water for three times, and then dry it at 105° C. The product obtained after drying is iron-modified waste residue biochar.

[0025] Preferably, the heat treatment time is 1 to 3 hours.

[0026] Furthermore, as a preferred manner, the lignin-rich waste residue is pretreated lignin-rich waste residue, and the pretreatment includes crushing, screening and drying.

[0027] Furthermore, the mesh size of the sieving is 60 to 100 meshes.

[0028] Furthermore, the drying is performed at 80-105° C. for 24-48 hours.

[0029] Specifically, the pretreatment is to grind the lignin-rich waste residue, pass it through a 60-mesh sieve, and then dry it at 105° C. for 24 hours.

[0030] Furthermore, the sufficient impregnation is to subject the mixture of the lignin-rich waste residue and the iron salt solution to ultrasonic treatment and then to sufficient stirring.

[0031] Furthermore, the ultrasonic treatment is performed at a power of 80 to 120 W for 10 to 15 minutes.

[0032] Furthermore, the sufficient stirring is stirring at 450-550 rpm for 1-2 hours.

[0033] Furthermore, the protective gas of the protective atmosphere is selected from one or more of nitrogen, argon, helium and neon.

[0034] The present invention protects the iron-modified waste residue biochar prepared by the preparation method.

[0035] The present invention also protects the use of the iron-modified waste residue biochar in anaerobic digestion.

[0036] The present invention also protects a method for producing methane using organic waste, comprising the following steps: fully mixing anaerobic digestion with inoculum, adding the iron-modified waste residue biochar therein, and performing anaerobic digestion to produce methane;

[0037] Wherein, the mixing ratio of the iron-modified waste residue biochar and the anaerobic digestion substrate is (5-30):1g / L.

[0038] Preferably, the mixing ratio of the iron-modified waste residue biochar and the anaerobic digestion substrate is (5-20):1 g / L.

[0039] Furthermore, the anaerobic digestion substrate is organic wastewater and / or organic solid waste.

[0040] Organic wastewater is wastewater mainly composed of organic pollutants, usually from the paper, leather, food and other industries. Its organic matter concentration is high, which can easily cause eutrophication of water quality. These organic substances exist in the wastewater in a suspended or dissolved state and can be decomposed by the biochemical action of microorganisms, but a large amount of oxygen will be consumed in the decomposition process, resulting in a decrease in dissolved oxygen in the water, affecting the growth of aquatic organisms. In addition, due to its poor biodegradability and high chromaticity, this type of wastewater is difficult to treat and has great harm to the environment.

[0041] Organic solid waste refers to waste containing organic matter, including domestic waste, industrial waste, agricultural waste, etc. These wastes have complex components and potential environmental risks, contain a large amount of carbon elements, usually induce the growth of microorganisms such as bacteria and fungi, and have high biochemical activity.

[0042] Preferably, the mixing ratio of the organic wastewater and the organic solid waste is (0-100): (0-100) gSCOD: / gVS.

[0043] The mixing ratio here refers to the relative amount of organic wastewater and organic solid waste, expressed as gSCOD / gVS. Among them, gSCOD refers to the soluble chemical oxygen demand (Soluble Chemical Oxygen Demand) per gram of wastewater, which is an indicator of the content of organic matter in wastewater that can be oxidized by chemical oxidants (such as potassium dichromate), and the common unit is mg / L or g / L.

[0044] gVS: refers to the volatile solids content (Volatile Solids) in each gram of organic solid waste. It is an indicator to measure the content of organic matter in solid waste. The common unit is g / L.

[0045] When the mixing ratio is 100:0, it means that only organic wastewater is used in the treatment process, and no organic solid waste is used; when the mixing ratio is 0:100, it means that only organic solid waste is used in the treatment process, and no organic wastewater is used; when the mixing ratio is 75:25, it means that the mass ratio of SCOD content in organic wastewater to VS content in organic solid waste is 75:25; (0~100): (0~100): means that the mixing ratio of organic wastewater and organic solid waste in the treatment process can be adjusted arbitrarily within this range, which covers all situations of using only wastewater, only solid waste and a mixture of the two.

[0046] Preferably, the mixing ratio of the cellulosic ethanol refining wastewater and pig manure is (25-75): (25-75) gSCOD / gVS.

[0047] More preferably, the mixing ratio of the cellulosic ethanol refining wastewater and pig manure is (50-75): 1 gSCOD / gVS.

[0048] Preferably, the organic wastewater comprises cellulosic ethanol refining wastewater, which is derived from the mash discharged after ethanol distillation, and the wastewater with high organic matter content is obtained after solid-liquid separation.

[0049] Preferably, the organic solid waste includes one or more types of livestock manure.

[0050] Preferably, the livestock manure includes one or more of pig manure, chicken manure, cow manure, sheep manure and duck manure.

[0051] More preferably, the anaerobic digestion substrate is cellulosic ethanol refinery wastewater and pig manure, wherein pig manure has the characteristics of large output, low collection and storage cost, and is rich in nitrogen. Mixing with refinery wastewater can effectively adjust the substrate C / N.

[0052] Furthermore, the SCOD of the anaerobic digestion substrate is 40-200 g / L.

[0053] Preferably, the SCOD of the anaerobic digestion substrate is 60-150 g / L.

[0054] Furthermore, the ammonia nitrogen content of the anaerobic digestion substrate is 60 to 2000 mg / L.

[0055] Preferably, the ammonia nitrogen content of the anaerobic digestion substrate is 300-1500 mg / L.

[0056] Preferably, the mixing ratio of the cellulosic ethanol refining wastewater and pig manure is (25-75): (25-75) gSCOD / gVS.

[0057] More preferably, the mixing ratio of the cellulosic ethanol refinery wastewater and pig manure is (50-75): 1 gSCOD / gVS. The digestion of cellulosic ethanol refinery wastewater and pig manure at this mixing ratio has a better synergistic effect.

[0058] More preferably, the mixing ratio of the iron-modified waste residue biochar and the anaerobic digestion substrate is (10-20): 1 g / L.

[0059] Furthermore, the inoculum is an anaerobic activated sludge composed of anaerobic digestion microorganisms, suspended matter and colloidal matter, which can be purchased commercially or homemade. This application mainly explores the addition of modified waste residue biochar to the substrate to enhance the methane production capacity of anaerobic digestion. This application does not set any special requirements for the use of inoculum, and conventional anaerobic activated sludge can meet the experimental needs.

[0060] As a preferred embodiment, the inoculum is anaerobic activated sludge obtained by natural fermentation and cultivation of food waste and sludge in an anaerobic reactor.

[0061] Furthermore, the VS content in the inoculum is 3-6wt%.

[0062] Furthermore, the mixing ratio of the anaerobic digestion substrate to the inoculum is 1:(0.2-2) (based on VS), that is, the above mixing ratio means that the mass ratio of the VS content in the anaerobic digestion substrate to the VS content in the inoculum is 1:(0.2-2).

[0063] Preferably, the mixing ratio of the anaerobic digestion substrate to the inoculum is 1:(0.8-1.5) (based on VS).

[0064] As a more preferred embodiment, the mixing ratio of the anaerobic digestion substrate to the inoculum is 1:1 (based on VS).

[0065] Preferably, the temperature of anaerobic digestion to produce methane is 25-40°C.

[0066] More preferably, the temperature of anaerobic digestion to produce methane is 32-38°C.

[0067] As a most preferred embodiment, the temperature of anaerobic digestion to produce methane is 35-37°C.

[0068] Preferably, the stirring shaft speed of the anaerobic digestion and methane production reactor is 60-120 rpm.

[0069] Compared with the prior art, the present invention has the following beneficial effects:

[0070] (1) The present invention mixes lignin-rich waste residue with a specific iron salt solution, obtains a carbon precursor by an impregnation method, and promotes the pyrolysis of biomass to form a graphitized structure through pyrolysis and calcination to obtain a modified waste residue biochar loaded with Fe. The obtained iron-modified waste residue biochar is added to an anaerobic digestion system with organic waste as a substrate, which can not only utilize the strong adsorption and buffering capacity of biochar to enhance the stability of the anaerobic system, but also the Fe loaded on the surface of the iron-modified waste residue biochar can act as an electron mediator to enhance the activity of related enzymes in the anaerobic system, while enhancing the electrochemical properties of biochar, and can also provide microorganisms with the trace elements required for growth, improve the digestion efficiency of the system, thereby increasing the total methane production of anaerobic digestion of wastewater, and can achieve harmless treatment and resource utilization of organic waste.

[0071] (2) The present invention further selects cellulosic ethanol refining wastewater as an organic wastewater mixed with organic solid waste as an anaerobic digestion substrate, and uses cellulosic ethanol refining waste residue as a lignin-rich waste residue to prepare modified cellulosic waste residue biochar, which is added to the mixed anaerobic digestion system of cellulosic ethanol refining wastewater and nitrogen-rich organic solid waste. This can effectively improve the performance of the wastewater anaerobic co-digestion system and increase the methane yield, thereby realizing the closed-loop utilization of cellulosic refining waste. BRIEF DESCRIPTION OF THE DRAWINGS

[0072] Figure 1 Statistical graphs of daily (a) and cumulative (b) methane yields from enhanced anaerobic co-digestion of waste residue biochar prepared at different temperatures.

[0073] Figure 2 This is the process flow chart for enhanced anaerobic co-digestion of iron salt modified waste residue biochar.

[0074] Figure 3 Statistical graphs of daily (a) and cumulative (b) methane yields from enhanced anaerobic co-digestion of waste residue biochar modified with different iron salts.

[0075] Figure 4 Statistical graphs of daily (a) and cumulative (b) methane yields of anaerobic co-digestion enhanced by different doses of ferric citrate modified carbon (CABC). DETAILED DESCRIPTION

[0076] The present invention is further described below in conjunction with the accompanying drawings and specific examples, but the examples do not limit the present invention in any form. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art.

[0077] Unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0078] Figure 1 (a) indicates Figure 1 In Figure (a), Figure 3 (a) Representation Figure 3 The naming meanings of other figures are similar to Figure (a) in the figure.

[0079] Example 1 Experimental study on anaerobic digestion of refinery wastewater mixed with two nitrogen-rich substrates in different proportions

[0080] 1. Experimental methods

[0081] Anaerobic digestion of mixed substrates for gas production: The cellulose ethanol refining wastewater used as the raw materials for anaerobic digestion comes from Hebei Yigao Bioenergy Co., Ltd., pig manure comes from Heshan Green Lake Bioenergy Co., Ltd., and food waste comes from Guangdong Green Profit Environmental Technology Co., Ltd. The SCOD and ammonia nitrogen concentrations of the wastewater are 96800 mg / L and 76.5 mg / L, respectively, and the volatile solids (VS) of pig manure and food waste are 17.23% and 21.39%, respectively, and the ammonia nitrogen concentrations are 1730.0 mg / L and 531.5 mg / L, respectively. The wastewater and the two nitrogen-rich organic solid wastes are mixed evenly at 100:0, 75:25, 50:50, 25:75, and 0:100 (gSCOD:gVS), and then the mixed digestion substrate and the inoculum are loaded into the anaerobic reactor at a ratio of 1:1 (based on VS). The reactor stirring shaft speed is set to 60 rpm for regular stirring, and anaerobic digestion is carried out in a 36°C constant temperature water bath to produce biogas. The inoculum is anaerobic activated sludge composed of anaerobic digestion microorganisms, suspended matter and colloidal matter. It was obtained by natural anaerobic fermentation of kitchen waste and sludge in an anaerobic reactor under medium temperature conditions (36±1℃) (no additional inoculation of specific anaerobic microorganisms is required), and the VS is 4.18wt%.

[0082] The methane production during anaerobic digestion was monitored and standardized using the Gas Endeavour instrument. The synergy index of mixed fermentation was calculated by comparing the methane production data of two different digestion substrates digested separately. The calculation formula of the synergy index is as follows:

[0083] Synergy index = methane production of mixed substrates / (methane production of A substrate digested alone*A substrate proportion+methane production of B substrate digested alone*B substrate proportion)

[0084] Table 1 Basic properties of raw materials

[0085]

[0086] 2. Experimental results

[0087] Table 2 Synergy index of anaerobic digestion of refinery wastewater, pig manure and restaurant kitchen waste

[0088]

[0089] The methane production of each reactor in the anaerobic digestion experiment of refining wastewater mixed with two nitrogen-rich substrates in different proportions is shown in Table 2. As can be seen from the table, the synergy index of the refining wastewater and pig manure group is generally higher than that of the refining wastewater and kitchen group, which shows that the mixed digestion of refining wastewater and pig manure has a better synergistic effect. Among them, the methane production of the mixture of refining wastewater and pig manure in a ratio of 75:25 (gSCOD:gVS) was the highest, which was 9.72% higher than the R1 group and 30.41% higher than the R5 group, which shows that the mixed substrate combination has the best effect on improving methane production for anaerobic digestion.

[0090] Example 2 Cellulosic ethanol refining waste residue biochar prepared at different temperatures and its application in anaerobic digestion gas production

[0091] 1. Experimental methods

[0092] (1) Preparation of biochar from cellulosic ethanol refining waste residue

[0093] The cellulose ethanol refining waste residue was obtained from Hebei Yigao Bioenergy Co., Ltd., and its cellulose and lignin contents were 9.88% and 70.57%, respectively. The cellulose ethanol refining waste residue was crushed and passed through a 60-mesh sieve, and then dried for 24 hours; the dried cellulose ethanol refining waste residue was placed in a tubular furnace in an oxygen-free atmosphere and heat treated at 400, 500, 600, 700, and 800°C for 2 hours, respectively, with a heating rate of 10°C / min. After the treatment, it was cooled to room temperature, washed three times with anhydrous ethanol and deionized water through a vacuum filtration device, and then dried to obtain biochar BC400-800.

[0094] (2) Anaerobic digestion gas production

[0095] The raw materials for anaerobic digestion are cellulose ethanol refining wastewater and pig manure, which are taken from Hebei Yigao Bioenergy Co., Ltd. and Heshan Green Lake Bioenergy Co., Ltd. respectively. The wastewater and pig manure are mixed evenly at a ratio of 75:25 (gSCOD:gVS). The SCOD of the mixed substrate is 83600 mg / L and the ammonia nitrogen concentration is 489.50 mg / L. Then the mixed digestion substrate and the inoculum are loaded into the anaerobic reactor at a ratio of 1:1 (based on VS). The reactor stirring shaft speed is set to 60 rpm and stirred regularly. Anaerobic digestion is carried out in a constant temperature water bath at 36°C to produce biogas. The inoculum is an anaerobic activated sludge composed of anaerobic digestion microorganisms, suspended matter and colloidal matter. It is obtained by the anaerobic digestion laboratory of the Institute of Biomass Engineering of A University under medium temperature conditions (36±1°C) using natural anaerobic fermentation of food waste and sludge in an anaerobic reactor, and the VS is 5.44wt%.

[0096] Methane production during anaerobic digestion was monitored and standardized using the BIPGAS Endeavour instrument.

[0097] 2. Experimental results

[0098] The methane production of each reactor in the anaerobic digestion experiment of wastewater and pig manure is as follows Figure 1 As shown in Figure 2, each experimental group showed a similar methane production trend. The second methane production peak of the reactor with biochar added was 2 to 3 days earlier than that of the control group (see Figure 1 (a)). The cumulative methane yields of the experimental groups with biochar addition were BC400 (255.67 mL / gVS), BC500 (252.41 mL / gVS), BC600 (214.32 mL / gVS), BC700 (209.66 mL / gVS), and BC800 (197.35 mL / gVS) (see Figure 1 (b)), relative to the control group (221.83 mL / gVS), the enhancement effects were BC400 (15.25%), BC500 (13.78%), BC600 (-3.39%), BC700 (-5.49%), and BC800 (-11.04%), that is, the addition of biochar prepared at 400-500 °C can increase methane production, among which the addition of biochar BC400 prepared at 400 °C has the best effect on increasing methane production.

[0099] Example 3 Biochars from cellulosic ethanol refining waste residues modified by different iron salts and their application in anaerobic digestion gas production

[0100] 1. Experimental methods

[0101] (1) Preparation of biochar from cellulosic ethanol refining waste residue modified by different iron salts

[0102] Cellulosic ethanol refining waste residue was obtained from Hebei Yigao Bioenergy Co., Ltd., and its cellulose and lignin contents were 9.88% and 70.57%, respectively. Various iron salts were mixed with cellulosic ethanol refining waste residue in a mass ratio of 1:10, added to deionized water, and subjected to 100W power ultrasonic treatment for 10 minutes, stirred with a magnetic stirrer for 1 hour, and dried for 24 hours to obtain an iron-modified carbon precursor; the carbon precursor was placed in a tubular furnace in an oxygen-free atmosphere and heat treated at 400°C for 2 hours at a heating rate of 10°C / min. After the treatment, it was cooled to room temperature, filtered and washed three times with anhydrous ethanol and deionized water, and dried to obtain iron-modified waste residue biochar.

[0103] (2) Anaerobic digestion gas production

[0104] The raw materials for anaerobic digestion are cellulose ethanol refining wastewater and pig manure, which are taken from Hebei Yigao Bioenergy Co., Ltd. and Heshan Green Lake Bioenergy Co., Ltd. respectively. The wastewater and pig manure are mixed evenly at a ratio of 75:25 (gSCOD:gVS). The SCOD of the mixed substrate is 83600 mg / L, and the ammonia nitrogen concentration is 489.50 mg / L. Then the mixed digestion substrate and the inoculum are loaded into the anaerobic reactor at a ratio of 1:1 (based on VS), and 10 g / L of different iron-modified cellulose waste biochars are added and marked as R1 to 6 respectively. The reactor stirring shaft speed is set to 60 rpm and stirred regularly. Anaerobic digestion is carried out in a constant temperature water bath at 36 ° C to produce biogas. The process flow is as follows: Figure 2 The inoculum is anaerobic activated sludge composed of anaerobic digestion microorganisms, suspended matter and colloidal matter, which was obtained by natural anaerobic fermentation of kitchen waste and sludge in an anaerobic reactor under medium temperature conditions (36±1℃) in the Anaerobic Digestion Laboratory of Biomass Engineering Institute of University A, with a VS of 3.19wt%.

[0105] Among them, R1-6 represent cellulosic waste biochar modified by different iron salts, R1: ferric chloride, R2: ferric sulfate, R3: ferric nitrate, R4: ferrous chloride, R5: ferrous sulfate, R6: ferric citrate. That is, R1 represents cellulosic waste biochar modified by ferric chloride, and the meanings of other names are similar.

[0106] The volume of methane produced by anaerobic digestion was monitored in real time and standardized using the Gas Endeavour instrument.

[0107] 2. Experimental results

[0108] The results of the experiment on the anaerobic digestion of waste liquid and pig manure enhanced by biochar modified with different iron salts are as follows: Figure 3 As shown. In the AD (anaerobic digestion reactor) system, the total digestion time is 35 days. Most anaerobic reactors enter the peak period of methane production in 6 to 12 days, while the R2 and R5 sulfate-modified enhanced groups enter the peak period of methane production after 16 days ( Figure 3(a)). The gas production then gradually decreased and fell to less than 1% of the total gas production on days 32 to 35. The cumulative methane production of each group was R1 (221.53±3.04mL / gVS), R2 (314.17±3.15mL / gVS), R3 (264.45±9.21mL / g VS), R4 (301.06±4.67mL / gVS), R5 (307.63±9.61mL / gVS), and R6 (338.53±7.48mL / gVS), which were -29.65%, -0.07%, -16.01%, -4.39%, -2.30%, and 7.52% higher than those of the unloaded biochar control (i.e. BC400) group (314.87±2.29mL / gVS), and -24.76%, 6.86%, -10.18%, 2.25%, 4.48%, and 14.98% higher than those of the no-addition digestion (without adding any biochar, i.e. Control group) group (294.43±1.94mL / gVS). It can be seen that the daily methane production rate of the biochar group modified by ferric citrate (i.e., R6 group) not only peaked earlier than that of the Control group and BC400 group, but also its final cumulative methane production rate showed a significant increase in production ( Figure 3 (b)). This indicates that biochar modified with ferric citrate can maximize the combined advantages of iron and biochar, so that biochar modified with ferric citrate should be able to significantly increase the methane production rate of the system.

[0109] Example 4 Effect of different amounts of iron salt-modified biochar additives on anaerobic digestion gas production

[0110] 1. Experimental methods

[0111] (1) Preparation of ferric citrate modified biochar (CABC)

[0112] The cellulose ethanol refining waste residue was obtained from Hebei Yigao Bioenergy Co., Ltd., and its cellulose and lignin contents were 9.88% and 70.57%, respectively. Ferric citrate and cellulose waste residue were mixed in a mass ratio of 1:10 and added to deionized water. After ultrasonic treatment at 100W power for 10 minutes, stirred with a magnetic stirrer for 1 hour, and dried for 24 hours, an iron-modified carbon precursor was obtained; the carbon precursor was placed in a tubular furnace in an oxygen-free atmosphere and heat treated at 400℃ for 2 hours with a heating rate of 10℃ / min. After the treatment, it was cooled to room temperature, filtered and washed three times with anhydrous ethanol and deionized water, and dried to obtain CABC.

[0113] (2) Anaerobic digestion gas production with different additive dosages

[0114] The raw materials for anaerobic digestion were cellulosic ethanol refining wastewater and pig manure, which were taken from Hebei Yigao Bioenergy Co., Ltd. and Heshan Green Lake Bioenergy Co., Ltd., respectively. The wastewater and pig manure were mixed evenly at a ratio of 75:25 (gSCOD:gVS), and the SCOD of the mixed substrate was 83600 mg / L, and the ammonia nitrogen concentration was 489.50 mg / L. The wastewater and pig manure were mixed evenly at a ratio of 75:25 (gSCOD:gVS), and then the mixed digestion substrate and inoculum were loaded into the anaerobic reactor at a ratio of 1:1 (based on VS), and 5, 10, 20, and 40 g / L of CABC were added respectively (the reactors were marked as CABC (5) to CABC (40) respectively). The reactor stirring shaft speed was set to 60 rpm for regular stirring, and anaerobic digestion was carried out in a constant temperature water bath at 36 °C to produce biogas. The inoculum is anaerobic activated sludge composed of anaerobic digestion microorganisms, suspended matter and colloidal matter. It was obtained by natural anaerobic fermentation culture of kitchen waste and sludge in an anaerobic reactor under medium temperature conditions (36±1℃) in the Anaerobic Digestion Laboratory of the Institute of Biomass Engineering of University A, with a VS of 5.72wt%.

[0115] The volume of methane produced by anaerobic digestion was monitored in real time and standardized using the Gas Endeavour instrument.

[0116] 2. Experimental results

[0117] The results of methane yield in the anaerobic digestion experiment of pig manure with different dosages of CABC are shown in the figure. Figure 4 As shown. With the change of CABC dosage, the order of cumulative methane yield is CABC (10) (247.00 ± 1.63 mL / gVS) > CABC (20) (238.94 ± 4.15 mL / gVS) > CABC (5) (237.55 ± 3.07 mL / gVS) > BC400 (10) (228.17 ± 3.62 mL / gVS) > Control (212.40 ± 1.06 mL / gVS) > CABC (40) ( 200.67±9.43mL / gVS), among which the reactors with CABC added increased CABC(5)(11.84%), CABC(10)(16.29%), CABC(20)(12.49%), and CABC(40)(-5.53%) respectively compared with the control group without addition. With the increase of CABC additive amount, the methane yield showed a trend of first increasing and then decreasing, and the anaerobic reactor with CABC added at a concentration of 10g / L showed the highest methane yield. This shows that only when the appropriate amount of CABC additive is added can the methane yield be increased in the coordinated anaerobic digestion.

[0118] In summary, the present invention mixes lignin-rich waste residue with a specific iron salt-ferric citrate solution, obtains a carbon precursor by an impregnation method, promotes the pyrolysis of biomass to form a graphitized structure through pyrolysis and calcination, and obtains a modified waste residue biochar loaded with Fe. The obtained iron-modified waste residue biochar is added to an anaerobic digestion system with organic waste as a substrate, which can not only utilize the strong adsorption and buffering capacity of biochar to enhance the stability of the anaerobic system, but also the Fe loaded on the surface of the iron-modified waste residue biochar can be used as an electron mediator to enhance the activity of related enzymes in the anaerobic system, while enhancing the electrochemical properties of biochar, and can also provide microorganisms with the trace elements required for growth. The combination of ferric citrate and waste residue biochar can maximize the combined advantages of iron and biochar, improve the digestion efficiency of the system, thereby increasing the total methane production of anaerobic digestion of wastewater, and can achieve harmless treatment and resource utilization of organic waste.

[0119] The present invention further selects cellulosic ethanol refining wastewater as an organic wastewater mixed with organic solid waste as an anaerobic digestion substrate, and utilizes cellulosic ethanol refining waste residue as lignin-rich waste residue to prepare modified cellulosic waste residue biochar, which is added to the mixed anaerobic digestion system of cellulosic ethanol refining wastewater and nitrogen-rich organic solid waste, which can effectively improve the performance of the wastewater anaerobic co-digestion system and increase the methane yield, thereby realizing the closed-loop utilization of cellulose refining waste.

[0120] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A method for preparing iron-modified waste residue biochar, characterized in that: The steps include: S1. The lignin-rich waste residue is fully impregnated in an iron salt solution and dried to obtain an iron-modified carbon precursor; S2. The obtained iron-modified carbon precursor is heat-treated at 400-700° C. in a protective atmosphere, fully calcined, and post-treated to obtain iron-modified waste residue biochar; Wherein, the cellulose content in the lignin-rich waste residue is ≥9%, and the lignin content is ≥50%; The iron salt is selected from ferric citrate or its hydrate.

2. The preparation method according to claim 1, characterized in that: The lignin-rich waste residue is cellulose ethanol refining waste residue.

3. The preparation method according to claim 1, characterized in that: The mass ratio of the iron salt to the lignin-rich waste residue is 1:(8-15).

4. Iron-modified waste residue biochar prepared by the preparation method according to any one of claims 1 to 4.

5. Use of the iron-modified waste residue biochar according to claim 4 in anaerobic digestion.

6. A method for producing methane using organic waste, characterized in that: The method comprises the following steps: fully mixing the anaerobic digestion substrate and the inoculum, adding the iron-modified waste residue biochar according to claim 4 thereto, and performing anaerobic digestion to produce methane; Wherein, the mixing ratio of the iron-modified waste residue biochar and the anaerobic digestion substrate is (5-30):1g / L.

7. The method according to claim 6, characterized in that: The anaerobic digestion substrate is organic wastewater and / or organic solid waste.

8. The method according to claim 6, characterized in that: The organic wastewater includes cellulosic ethanol refining wastewater.

9. The method according to claim 6, characterized in that: The organic solid waste includes one or more of livestock manure, food waste, and agricultural and forestry waste.

10. The method according to claim 6, characterized in that: The livestock manure includes one or more of pig manure, chicken manure, cow manure, sheep manure and duck manure.

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