Method for increasing biogas yield by pretreating coal gangue with desilicication bacteria

Abstract

The invention belongs to the field of ecological utilization of coal-based solid waste, and particularly relates to a method for treating coal gangue by using desilicication bacteria to promote methane production from the coal gangue, which comprises the following steps: 1, culturing the desilicication bacteria (bacillus mucilaginosus); 2, pretreatment of coal gangue; 3, optimizing conditions for treating the coal gangue by the desilicication bacteria; 4, collecting the coal gangue treated by the desilicication bacteria; and 5, carrying out a biological gas production test by taking the coal gangue treated by the desilicication bacteria and untreated coal gangue as substrates. The coal gangue is subjected to desilicication treatment, so that the gas production rate can be increased by nearly three times.

Description

Technical Field

[0001] This invention belongs to the field of biomass coalbed methane, specifically relating to a method for promoting biogas production from coal gangue by pretreating it with desilication bacteria. Background Technology

[0002] Biomass gas refers to methane-based gas produced in coal seams through the metabolic activities of microorganisms that convert organic matter into methane. Essentially, this is a biochemical process driven by microorganisms. Microorganisms utilize substrates in the coal seam (such as organic components like cellulose, hemicellulose, and lignin) for anaerobic fermentation and other reactions, ultimately producing methane. The formation of biomass gas is the result of the synergistic action of multiple microorganisms, including acid-producing bacteria such as Clostridium (…). Clostridium Bacteria such as *Methanobacterium* play a crucial role in the hydrolysis and acid production stages. These bacteria can secrete various hydrolytic enzymes to break down complex organic matter in coal seams into small-molecule organic acids and alcohols, providing substrates for methanogens. Methanogens mainly include the genus *Methanobacterium*. Methanobacterium ), Methanococcus spp. Methanococcus These are the core microorganisms that produce methane, utilizing substrates produced by acid-producing bacteria to generate methane through specific metabolic pathways. Methanogens are strict anaerobes, highly sensitive to environmental conditions such as oxygen levels and pH values.

[0003] Coal gangue is a solid waste generated during coal mining, washing, and processing. It is a rock associated with coal, primarily composed of minerals such as kaolin, quartz, feldspar, mica, and carbonaceous shale, as well as small amounts of metallic elements like aluminum, iron, calcium, and magnesium. In my country, coal gangue production accounts for approximately 10%-15% of raw coal production, with annual emissions exceeding 700 million tons and accumulated stockpiles of about 7 billion tons. Currently, the utilization of coal gangue mainly includes the building materials sector (e.g., brick making, cement production, ceramics manufacturing); the energy sector (e.g., power generation); and land reclamation and ecological restoration (e.g., filling subsidence areas, soil improvement). Coal gangue contains some components that can be utilized by microorganisms. Under suitable conditions, microorganisms can decompose the organic components in coal gangue to produce gases. Some anaerobic microorganisms can decompose cellulose and hemicellulose in coal gangue, producing methane and carbon dioxide through fermentation. Methanogenic bacteria use intermediate products such as organic acids, hydrogen, and carbon dioxide produced during fermentation to generate methane.

[0004] The silicate content in coal gangue is generally between 40% and 70%, mainly composed of quartz and plagioclase. Silicates in coal gangue may inhibit biogas production. Some organic matter in coal gangue coexists with silicates during sedimentary diagenesis, forming an "organic-inorganic complex." Silicates may also encapsulate residual organic matter in coal gangue, hindering microbial contact and degradation. Anaerobic digestion requires extracellular enzymes secreted by microorganisms to contact organic matter. Silicate encapsulation prevents enzymes from effectively binding substrates, reducing the hydrolysis rate. Simultaneously, the microporous structure of silicates traps small-molecule organic acids, hindering their diffusion to methanogenic bacterial communities. The negatively charged surface of silicates can adsorb cations required by methanogenic or hydrolytic bacteria, affecting methanogenic activity. Dissolution of silicates may release SiO3. 2- Raising the system pH beyond the suitable range for methanogens can lead to problems. Certain silicates may act as electron acceptors, competing with methanogens for substrates. Currently, various physical, chemical, biological, and combined treatment methods have been developed to address the issue of silicates in coal gangue reducing biogas production efficiency. These methods aim to disrupt silicate encapsulation structures, release organic matter, and optimize microbial activity. Physical pretreatment methods mainly include mechanical crushing / grinding, heat treatment, and ultrasonic treatment. Mechanical crushing / grinding is not only energy-intensive but may also carbonize organic matter during high-temperature calcination. Ultrasonic treatment is costly, limited in large-scale application, only partially disrupts the encapsulation structure, and has limited effectiveness on some dense silicates. Chemical treatment methods mainly include acid treatment and alkali treatment. Chemical treatment methods use strong acids / alkalis that corrode equipment, requiring corrosion-resistant materials, incurring high chemical costs, posing a risk of secondary pollution, and potentially inhibiting subsequent microbial activity. Biological treatment methods utilize microorganisms or enzymes to decompose silicate structures, releasing encapsulated organic matter and improving biogas production efficiency. Biological treatment methods mainly include silicate bacteria treatment, iron-reducing bacteria treatment, and enzymatic-assisted treatment. Biological treatment utilizes microorganisms or enzymes to decompose silicate structures, releasing encapsulated organic matter and improving biogas production efficiency. Biological treatment offers advantages such as environmental friendliness, absence of chemical pollution, and the ability to specifically degrade particular silicate minerals, and was therefore adopted in this study. This research aims to utilize silicate bacteria to decompose silicate substances in coal gangue, reducing the silicate content and promoting biogas production from coal gangue. Summary of the Invention

[0005] The purpose of this invention is to provide a method for increasing methane production by treating coal gangue with desilication bacteria, so as to effectively increase methane production in the biogas production process of coal gangue and realize the efficient resource utilization of coal gangue.

[0006] The specific technical solution adopted by this invention is as follows: A method for increasing methane production by treating coal gangue with desilication bacteria includes the following steps: Step 1: Cultivation of desilicifying bacteria (Bacillus mucilaginosus); Step 2: Pretreatment of coal gangue; Step 3: Desilication bacteria treatment of coal gangue; Step 4: Collect and process the coal gangue after desilication bacteria treatment; Step 5: Biogas production is carried out using coal gangue treated with desilication bacteria and untreated coal gangue as substrates.

[0007] The strain is Bacillus mucilaginosus (Bacillus mucilaginosus). Bacillus mucilaginosus Krassilnikov), accession number ACCC 19749.

[0008] Specifically, desilication bacteria were inoculated into a liquid culture medium and activated at 28-30℃ and 150-200 rpm to obtain a bacterial suspension. The liquid culture medium contained: 10.0 g / L sucrose, 2.0 g / L K₂HPO₄, 0.5 g / L MgSO₄, 0.5 g / L yeast extract, 1.0 g / L (NH₄)₂SO₄, 0.1 g / L NaCl, and 0.1 g / L CaCO₃, with a pH of 7.0-7.2.

[0009] The silicate content of coal gangue is 40%-70%. The pretreatment steps include: breaking the sample into small pieces, crushing it with a high-speed universal pulverizer, and then sieving it to obtain coal gangue with a mesh size of less than 200.

[0010] In the process of treating coal gangue with desilication bacteria, the bacterial solution obtained in the first step is mixed with the coal gangue pretreated in the second step, and a culture medium is added. The mixture is then cultured for 10-30 days at 28℃-30℃ and 150rpm-200rpm. The culture medium has a pH of 4-8, uses yeast powder as the nitrogen source, and adds 20-100g / L of coal gangue.

[0011] More preferably, the culture medium has a pH of 7, uses yeast powder as the nitrogen source, and adds 80 g / L of coal gangue (solid-liquid ratio of 1:12.5).

[0012] After desilication treatment, the lime content of coal gangue is reduced by 2%-5%, the volatile matter is increased by 1.5%-3%, and the biological desilication rate reaches 30%-35%.

[0013] The fifth step of the biogas production process is as follows: using the coal gangue obtained in step (4) as a substrate, inoculate it with a mixed methanogenic bacterial group, culture it in an anaerobic medium at 35-40℃ for 45-60 days, and collect the methane; the anaerobic medium contains: MgCl2 0.2 g / L, NaCl 1.0 g / L, KCl 0.4 g / L, NH4Cl 2.0 g / L, and adds trace elements and vitamins.

[0014] The methanogenic mixed microbial community was passaged from sludge, and its culture medium contained per liter of: 15 mg of nitroglycerin, 1.8 mg of CoCl2·6H2O, 1 mg of FeSO4·7H2O, 1.8 mg of ZnSO4·7H2O, 5 mg of MnSO4·H2O, 0.1 mg of Na2MoO4·2H2O, 0.3 mg of NiCl2·6H2O, 0.1 mg of CuSO4·5H2O, 0.2 mg of KAl(SO4)2·12H2O, and 0.1 mg of H3BO3; as well as 0.1 mg of pyridoxine hydrochloride, 0.05 mg of calcium pantothenate, 0.05 mg of thiamine, 0.05 mg of riboflavin, 0.05 mg of nicotinic acid, 0.05 mg of para-aminobenzoic acid, 0.05 mg of lipoic acid, 0.02 mg of folic acid, 0.02 mg of biotin, and 0.001 mg of cobalamin.

[0015] The technical effects achieved by this invention are as follows: The amount of methane produced by biogas production from coal gangue treated with silicate bacteria is three times that of untreated coal gangue.

[0016] Treating coal gangue with desilication bacteria can remove siliceous minerals from the gangue, improve the accessibility of organic matter in the gangue for methanogens, and thus significantly increase methane production. This method is simple to operate, low in cost, and environmentally friendly, making it suitable for large-scale application in coal gangue treatment and biogas production processes. Attached Figure Description

[0017] Figure 1 Graph showing changes in biomethane production. Detailed Implementation

[0018] To make the objectives and advantages of this invention clearer, the invention will be specifically described below with reference to embodiments. It should be understood that the following text is merely used to describe one or more specific embodiments of the invention and does not strictly limit the scope of protection specifically claimed by the invention.

[0019] Step 1: Cultivation of desilicifying bacteria (Bacillus mucilaginosus); The strain used in this experiment was Bacillus mucilaginosus (Bacillus mucilaginosus). Bacillus mucilaginosus Krassilnikov (accession number ACCC 19749), purchased from Qiangxing Biotechnology Co., Ltd. (product form: freeze-dried powder). The original depository of this strain is the Agricultural Culture Collection of China (ACCC).

[0020] The formula for the silicate bacteria liquid culture medium is as follows: Add 10.0 g sucrose, 2.0 g dipotassium hydrogen phosphate, 0.5 g magnesium sulfate, 0.5 g yeast extract, 1.0 g ammonium sulfate, 0.1 g sodium chloride, and 0.1 g calcium carbonate per liter of medium. Adjust the initial pH of the medium to 7.0-7.2 with dilute H₂SO₄ and NaOH solutions, and autoclave at 121℃ for 30 min. In a clean bench, take 100 mL of liquid culture medium and place it in a sterilized 250 mL plastic conical flask. Add 0.1 g of lyophilized powder to the medium and activate the bacteria in a benchtop constant-temperature shaker (shaker) at 180 rpm and 30℃. Store the expanded bacterial culture at 4℃.

[0021] Step 2: Pretreatment of coal gangue; The coal gangue used in this experiment was obtained from the roof gangue produced during the mining of the No. 6 coal seam in a coal mine in Inner Mongolia. First, the sample was broken into small pieces, then pulverized using a high-speed universal pulverizer. After pulverization, the gangue was sieved to obtain coal gangue with a mesh size of less than 200.

[0022] Step 3: Optimization of conditions for desilication bacteria treatment of coal gangue; To more effectively optimize the experimental conditions for silicate bacteria leaching and desilication, different nitrogen sources, pH values, and coal gangue addition amounts were set as the main influencing factors, and orthogonal experiments were conducted at five levels for each factor (Table 1).

[0023] The experiment was conducted in 250 mL plastic conical flasks, each containing 100 mL of the above-mentioned sterile silicate bacterial liquid culture medium (containing the corresponding nitrogen source) and a pre-set mass of coal gangue powder, aseptically inoculated at a 5% inoculum. The control conditions were 30±0.5℃, 150 rpm, with a leaching cycle of 14 days. 5 mL of leachate was aseptically collected every 48 h, and the concentration of the target element was detected using ICP-MS. Each experiment had three replicates to screen for the globally optimal parameter combination.

[0024] Table 1. Factor Level Table for Orthogonal Experiment Experiment No. Factor A (pH) Factor B (Nitrogen Source) Factor C (coal gangue addition amount / g) 1 4 Nitrogen-free 8 2 4 ammonium sulfate 10 3 4 Urea 2 4 4 peptone 4 5 4 yeast powder 6 6 5 ammonium sulfate 6 7 5 Urea 8 8 5 peptone 10 9 5 yeast powder 2 10 5 Nitrogen-free 4 11 6 ammonium sulfate 4 12 6 Urea 6 13 6 peptone 8 14 6 yeast powder 10 15 6 Nitrogen-free 2 16 7 ammonium sulfate 10 17 7 Urea 2 18 7 peptone 4 19 7 yeast powder 6 20 7 Nitrogen-free 8 21 8 ammonium sulfate 8 22 8 Urea 10 23 8 peptone 2 24 8 yeast powder 4 25 8 Nitrogen-free 6 The results of the orthogonal experiment are shown in Table 2.

[0025] Table 2. Results of the orthogonal experiment Experiment No. Factor A (pH) Factor B (Nitrogen Source) Factor C (Amount added / g) Silicon concentration (mg / L) 1 4 Nitrogen-free 8 32 2 4 ammonium sulfate 10 28 3 4 Urea 2 19 4 4 peptone 4 22 5 4 yeast powder 6 52 6 5 ammonium sulfate 6 29 7 5 Urea 8 69 8 5 peptone 10 54 9 5 yeast powder 2 28 10 5 Nitrogen-free 4 22 11 6 ammonium sulfate 4 31 12 6 Urea 6 89 13 6 peptone 8 92 14 6 yeast powder 10 117 15 6 Nitrogen-free 2 9 16 7 ammonium sulfate 10 54 17 7 Urea 2 48 18 7 peptone 4 87 19 7 yeast powder 6 134 20 7 Nitrogen-free 8 56 21 8 ammonium sulfate 8 58 22 8 Urea 10 77 23 8 peptone 2 24 24 8 yeast powder 4 79 25 8 Nitrogen-free 6 49 Table 3. Results of Intuitive Analysis

[0026] A direct analysis of the orthogonal experimental results reveals the following ranges: RA for factors A, B, and C are 42.00 and 6.20, respectively; RB is 42.0 and 6.00, respectively; and RC is 45.40 and 8.00, respectively. Based on the magnitude of the ranges, the order of importance of the factors is: RC > RB > RA, meaning that the amount added / g (factor C) has the greatest impact on silicon concentration, followed by pH value (factor A), while the nitrogen source (factor B) has the least impact. (Based on L...) 25 (5³) The orthogonal experiment yielded the optimal combination as A4B5C4. Therefore, for the silicon concentration in the supernatant, the optimal combination is pH=7, yeast powder as nitrogen source, and coal gangue added at 8 g (solid-liquid ratio 1:12.5).

[0027] Eight g of coal gangue from Roof No. 6 was weighed and added to 100 mL of sterile silicate bacteria liquid culture medium. One vial of bacterial culture in the logarithmic growth phase was taken, shaken well, and 5 mL of bacterial culture was added to each vial of slurry. The vials were then incubated for 15 days in a shaker at 180 rpm and 30℃. After 15 days of desilication treatment, the coal gangue was subjected to industrial analysis, elemental analysis, and X-ray photoelectron spectroscopy (XPS) analysis. The results are shown in Tables 4 and 5.

[0028] Table 4. Industrial and elemental analysis of coal gangue before and after desilication.

[0029] Table 5 XPS analysis of coal gangue before and after bioleaching

[0030] Therefore, the biological desilication rate can be calculated to be 31.9%.

[0031] Step 4: Collect the coal gangue after desilication bacteria treatment; After 15 days of shake-flask experiments, the coal gangue precipitate was collected by centrifugation (8000 rpm). First, the organic matter on the surface of the coal gangue was washed with anhydrous ethanol, and then the residual anhydrous ethanol was rinsed off with deionized water. The precipitate was then dried in an oven at 110℃ for 5 hours. After drying, the coal gangue was ground again for later use. Step 5: Biogas production using coal gangue treated with desilication bacteria as a substrate; Gas-producing substrate: 100g of coal gangue treated with Bacillus subtilis and 100g of coal gangue not treated with Bacillus subtilis; Microorganisms: Exogenous microorganisms were selected for the microbial sample. This mixed microbial community was a mixed microbial community passaged from sludge capable of producing methanogens; The formula of the mixed microbial culture medium was: 0.2g magnesium chloride, 1.0g sodium chloride, 0.4g potassium chloride, and 2.0g ammonium chloride per liter of culture medium; The trace element composition and addition amount of the culture medium were: 15mg nitric acid, 1.8mg cobalt chloride, 1mg ferrous sulfate heptahydrate, and 1.8mg zinc sulfate heptahydrate per liter. The culture medium contains: 5 mg manganese sulfate monohydrate, 0.1 mg sodium molybdate dihydrate, 0.3 mg nickel chloride hexahydrate, 0.1 mg copper sulfate pentahydrate, 0.2 mg potassium aluminum sulfate dodecahydrate, and 0.1 mg boric acid. The vitamin composition and dosage of the culture medium are as follows: per liter, add 0.1 mg pyridoxine hydrochloride, 0.05 mg calcium pantothenate, 0.05 mg thiamine, 0.05 mg riboflavin, 0.05 mg niacin, 0.05 mg para-aminobenzoic acid, 0.05 mg lipoic acid, 0.02 mg folic acid, 0.02 mg biotin, and 0.001 mg cobalamin.

[0032] The following steps were used to conduct the biogas production experiment: Prepare a mixed bacterial culture medium. After preparation, pour the medium into 300 mL anaerobic bottles, seal them with plastic film and rubber bands, and sterilize them in a high-temperature sterilizer. After sterilization, when the temperature drops to approximately 90 °C, wearing heat-resistant gloves, quickly place the anaerobic bottles into a pre-sterilized (15 min) laminar flow hood and immediately close the lids. When the temperature drops to approximately 40 °C, use a 10 mL syringe to add Na₂S·9H₂O filtered through a 0.22 μm sterile membrane and vitamins to the anaerobic bottles in the correct proportions. Since methanogens are anaerobic, sodium resazurin is used as an oxygen indicator. If the culture medium is pale pink, it indicates excessive oxygen and should not be used; if the medium is pale yellow, the oxygen content is negligible and it can be used for further experiments. Inoculate the mixed bacterial culture into 300 mL culture bottles and incubate them in an incubator at the appropriate temperature for 60 days. Starting from day 25, methane production is measured every 7 days. In this experiment, methane production remained essentially unchanged after 45 days. The gas production results are as follows: Figure 1 As shown, by Figure 1 It can be seen that the gas production effect of coal gangue after pretreatment with desilication bacteria is significantly better than that of untreated gangue.

Claims

1. A method for increasing biogas production by coal gangue pretreatment with desiliconization bacteria, characterized in that, The method comprises the following steps: (1) Culturing of desilication bacteria: inoculate the desilication bacteria into a liquid culture medium, and activate the culture at 28-30°C and 150-200 rpm to obtain a bacterial solution; (2) Coal gangue pretreatment: crush the coal gangue to below 200 mesh; (3) Desilication treatment: mix the bacterial solution obtained in step (1) with the coal gangue in step (2), add a culture medium, and culture at 28-30°C and 150-200 rpm for 10-30 days; (4) Collection of the treated coal gangue: centrifugation, anhydrous ethanol washing, deionized water rinsing, drying, and grinding for standby use; (5) Biological gas production: use the coal gangue obtained in step (4) as a substrate, inoculate a methanogenic mixed bacteria group, and culture in an anaerobic culture medium at 35-40°C for 45-60 days to collect methane.

2. The method of claim 1, wherein: The liquid culture medium in step 1) comprises 10.0 g / L sucrose, 2.0 g / L K2HPO4, 0.5 g / L MgSO4, 0.5 g / L yeast powder, 1.0 g / L (NH4)2SO4, 0.1 g / L NaCl, and 0.1 g / L CaCO3, and has a pH of 7.0-7.

2.

3. The method of claim 1, wherein: The desilicated bacteria in step 1) is Bacillus mucilaginosus (Bacillus mucilaginosus) Paenibacillus mucilaginosus ).

4. The method of claim 1, wherein: The silicate content of the coal gangue in step 2) is 40%-70%.

5. The method of claim 1, wherein: The inoculation amount of the bacterial solution in step 3) is 1-10%.

6. The method of claim 1, wherein: After the desilication treatment in step 3), the ash content of the coal gangue is reduced by 2%-5%, the volatile matter is increased by 1.5%-3%, and the biological desilication rate reaches 30%-35%.

7. The method of claim 1, wherein: The culture medium in step 3) has a pH of 4-8, the nitrogen source is yeast powder, and the addition amount of the coal gangue is 20-100 g / L of the culture medium.

8. The method of claim 1, wherein: The methanogenic mixed bacteria group in step (5) is subcultured from sludge, and the anaerobic culture medium comprises 0.2 g / L MgCl2, 1.0 g / L NaCl, 0.4 g / L KCl, and 2.0 g / L NH4Cl, and further comprises trace elements and vitamins, wherein the culture medium further comprises the following trace elements and vitamins per liter: 15 mg nitrilotriacetic acid, 1.8 mg CoCl2·6H2O, 1 mg FeSO4·7H2O, 1.8 mg ZnSO4·7H2O, 5 mg MnSO4·H2O, 0.1 mg Na2MoO4·2H2O, 0.3 mg NiCl2·6H2O, 0.1 mg CuSO4·5H2O, 0.2 mg KAl(SO4)2·12H2O, and 0.1 mg H3BO3; and 0.1 mg pyridoxine hydrochloride, 0.05 mg calcium pantothenate, 0.05 mg thiamine, 0.05 mg riboflavin, 0.05 mg nicotinic acid, 0.05 mg p-aminobenzoic acid, 0.05 mg lipoic acid, 0.02 mg folic acid, 0.02 mg biotin, and 0.001 mg cobalamin.

9. The method of claim 1, wherein: The culture medium in step 3) has a pH of 7, the nitrogen source is yeast powder, and the addition amount of the coal gangue is 80 g / L of the culture medium.

10. The use of the method of any one of claims 1-9 in the resource utilization of coal gangue or the production increase of biogas from abandoned coal mines.

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