Modified charcoal loaded ball-milled vulcanized zero-valent iron material as well as preparation method and application thereof

Abstract

The invention relates to a modified charcoal loaded ball-milled vulcanized zero-valent iron material as well as a preparation method and application thereof. The method comprises the following steps: carrying out chemical modification on ball-milled elemental sulfur and zero-valent iron to synthesize ball-milled vulcanized zero-valent iron; and then loading to straw biochar through chemical reaction to obtain the modified biochar loaded ball-milled vulcanized zero-valent iron composite material. In the starting period of anaerobic digestion of the high-temperature and high-solid-content sludge, a certain proportion of modified charcoal loaded ball-milled vulcanized zero-valent iron composite material is added into an anaerobic digestion reactor, the high-solid-content thermal hydrolysis-high-temperature anaerobic digestion efficiency can be remarkably improved, meanwhile, the acid accumulation effect affected by high temperature and high load is relieved, and the high-temperature anaerobic digestion efficiency is improved. Meanwhile, the biotoxicity of heavy metal Cr (VI, Cu, Cr and the like in the sludge is reduced, harmlessness, reduction and recycling of the municipal sludge are achieved, and the method has a wide application prospect in the aspect of municipal sludge treatment.

Description

Technical Field

[0001] The present invention belongs to the field of solid waste resource utilization, and particularly relates to a modified biochar-loaded ball-milled sulfided zero-valent iron material, and a preparation method and application thereof. Background Art

[0002] Sludge is the main by-product of sewage treatment plants. Sludge has the characteristics of large volume, high water content, and easy corruption. The commonly used sludge treatment processes include aerobic composting, concentrated dehydration, anaerobic digestion, incineration, drying, etc. Anaerobic digestion technology is widely used in the resource treatment of sludge. Its principle is to use anaerobic microorganisms to degrade organic matter in sludge under anaerobic conditions to produce biogas, carbon dioxide and water, and ultimately achieve the purpose of sludge reduction, harmlessness and resource utilization. The methane content of biogas produced by anaerobic digestion is about 55% to 70%, and the carbon dioxide content is about 30% to 45%. The low methane content seriously affects the recovery of biomass energy.

[0003] Compared with traditional anaerobic digestion technology, the use of thermal hydrolysis (75°C) high-temperature anaerobic digestion technology to treat high-solid sludge can significantly improve the degradation rate of organic matter in sludge and the production of biogas, shorten the hydraulic retention time, and further reduce the moisture content of biogas residue, which is conducive to the resource utilization of biogas residue. As an emerging sludge treatment process, thermal hydrolysis coupled with high-solid sludge anaerobic digestion technology has been widely used. However, during the anaerobic digestion process of high-solid sludge, a large amount of free ammonia will be produced due to the decomposition of organic matter, causing an imbalance in the methanogenic metabolic rate and accumulating a large amount of volatile organic acids. Studies have shown that ammonia concentrations exceeding 6000 mg / L will cause a decrease in the activity of methanogens, that is, ammonia inhibition. At the same time, the large accumulation of volatile fatty acids in the digestion system will also significantly inhibit the activity of methanogens. Summary of the invention

[0004] In order to overcome the drawbacks and shortcomings of the prior art, the main purpose of the present invention is to provide a modified biochar-loaded ball-milled sulfided zero-valent iron material and a preparation method and application thereof.

[0005] The purpose of the present invention is mainly achieved through the following solutions:

[0006] The present invention provides a method for preparing a modified biochar-loaded ball-milled sulfided zero-valent iron material, comprising:

[0007] (1) ball-milled elemental sulfur and original zero-valent iron are subjected to sulfurization modification to obtain ball-milled sulfurized zero-valent iron; a mixed solution of hydrochloric acid and polyethylene glycol is added to wheat straw powder, chemically modified by magnetic stirring, filtered and dried, and the obtained powder is placed in a tubular furnace for pyrolysis under anaerobic conditions, and naturally cooled to room temperature to obtain modified straw biochar;

[0008] (2) Add a mixed solution of NaBH4 and Na2S2O4 to the modified straw biochar and ball-milled zero-valent iron sulfide obtained in step (1), stir to allow for sufficient reaction, and obtain a modified biochar-loaded ball-milled zero-valent iron sulfide material after filtering, washing, and drying.

[0009] Preferably, in step (1), the original zero-valent iron and elemental sulfur are weighed and placed in a 304 stainless steel tank filled with Φ8 stainless steel beads, the stainless steel tank is fixed, and the parameters of the ball mill are set: forward rotation for 20 to 30 minutes, pause for 2 to 4 minutes, reverse rotation for 20 to 30 minutes, a total time of 120 to 150 minutes, and the rotation speed is 500 to 700 rpm.

[0010] More preferably, the ratio of sulfur content to iron content in elemental sulfur and original zero-valent iron is 0.16.

[0011] Preferably, in step (1), wheat straw powder is added to a mixed solution of hydrochloric acid and polyethylene glycol, magnetically stirred at a speed of 1200 rpm for 180 min for chemical modification, filtered and placed in an oven at 60° C. for drying, the mass volume ratio of the wheat straw powder to the mixed solution of hydrochloric acid and polyethylene glycol is 8:500 g / mL, and the concentration of polyethylene glycol in the mixed solution is 6 to 13 g / L.

[0012] Preferably, in step (1), the temperature rise program of pyrolysis is: the temperature rise rate is controlled at 5-8°C / min; after 120 minutes, the temperature is heated to 650°C, and the temperature is maintained for 180 minutes of pyrolysis before automatically entering the temperature drop program.

[0013] Preferably, in step (2), the mass ratio of NaBH4 and Na2S2O4 in the mixed solution of NaBH4 and Na2S2O4 is 6.07:1; the mass volume ratio of the total mass of the modified straw biochar and ball-milled zero-valent iron sulfide to the mixed solution of NaBH4 and Na2S2O4 is 1:15.6-17.2, and the mass ratio of the modified straw biochar and ball-milled zero-valent iron sulfide is 1:18.9-20.1.

[0014] The present invention also provides a modified biochar-loaded ball-milled sulfided zero-valent iron material, which is prepared by the above-mentioned preparation method.

[0015] The present invention further provides the use of the modified biochar-loaded ball-milled sulfidized zero-valent iron material in anaerobic digestion of high-temperature and high-solid sludge by thermal hydrolysis.

[0016] Preferably, at the initial stage of starting the anaerobic digestion reactor, the modified biochar-loaded ball-milled sulfided zero-valent iron is added to the anaerobic digestion reactor, the hydraulic retention time of the anaerobic digestion reactor is 2 to 5 days, the organic loading rate is 2.09 g / Ld, the operating temperature is set to 56±1°C, and the stirring rate is set to 110 r / min.

[0017] More preferably, the modified biochar loaded with ball-milled sulfidized zero-valent iron is added to the anaerobic digestion reactor 4 to 7 days after the anaerobic digestion reactor has been in operation.

[0018] Preferably, the amount of modified biochar-loaded ball-milled sulfidized zero-valent iron added is 1.32 to 2.06 g / L.

[0019] The present invention first puts the original zero-valent iron and elemental sulfur into a 304 stainless steel tank filled with Φ8 stainless steel beads, and obtains ball-milled sulfurized zero-valent iron after sulfurization modification by ball-milling elemental sulfur and zero-valent iron; the wheat straw biochar is subjected to high-temperature cracking under anaerobic conditions to obtain the original biochar. Subsequently, under magnetic stirring, the ball-milled sulfurized zero-valent iron is slowly added to a mixed solution of hydrochloric acid and polyethylene glycol of the biochar, and the modified biochar loaded with sulfurized zero-valent iron is successfully prepared after filtering, washing and drying. Subsequently, the modified biochar loaded with sulfurized zero-valent iron is added to a high-temperature, high-solid digestion reaction device, and the hydraulic retention time is set to 5d. The pH and CH4 content of the reactor are monitored every day, and the VFAs, COD, TSS concentrations of the digestate and the morphological distribution of heavy metals are measured every 3d. After the high-temperature, high-solid sludge anaerobic digestion reaction cycle is completed, the cumulative methane production is significantly increased, the acid accumulation and ammonia inhibition phenomena are significantly alleviated, and the biological toxicity of heavy metals is also significantly reduced. The present invention can not only increase the cumulative methane production, but also significantly alleviate the acid accumulation and ammonia inhibition phenomena that traditionally hinder high-temperature and high-solid content digestion operations, and improve the metabolic activity of microorganisms, while effectively reducing the heavy metal biological toxicity of the digested sludge, thereby facilitating the subsequent resource utilization of the sludge.

[0020] Compared with the prior art, the present invention has the following advantages and significant effects:

[0021] (1) The present invention uses ball-milled elemental sulfur to chemically modify zero-valent iron, which can significantly enhance the conductivity of the material, thereby improving the mobility of electrons and enhancing the reduction ability of the material.

[0022] (2) The present invention uses wheat straw biochar to load sulfidized zero-valent iron, which can significantly improve the defect that zero-valent iron is easy to agglomerate and reduces the reaction performance; at the same time, biochar has a large specific surface area, rich pore structure and functional groups, and can adsorb and complex with heavy metal ions in sludge to reduce the biological toxicity of heavy metals in sludge. It is conducive to achieving the "harmlessness, reduction and resource utilization" of municipal sludge, and has broad application prospects in municipal sludge treatment.

[0023] (3) The present invention utilizes a ball milling method to synthesize zero-valent iron sulfide, which can significantly increase its specific surface area and adsorption capacity, and improve its reaction activity, compared with the traditional preparation method.

[0024] (4) The present invention utilizes hydrochloric acid and polyethylene glycol to modify the biochar material, which is beneficial to increasing the loading capacity of the biochar material for zero-valent iron sulfide.

[0025] (5) The present invention adds modified biochar-loaded sulfide zero-valent iron material to the hot water hydrolysis coupled high-solid sludge anaerobic digestion process, which can significantly alleviate ammonia inhibition and organic acid accumulation, improve the conversion rate of sludge organic matter, and increase methane production. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a scanning electron microscope image of the modified biochar-loaded ball-milled sulfidized zero-valent iron material SZVI-BC in Example 1.

[0027] Figure 2 These are the test results of daily methane production of each test group in Example 2.

[0028] Figure 3 These are the test results of the changes in acetic acid concentration in the digestive fluid of each test group in Example 3.

[0029] Figure 4 These are the test results of the changes in propionic acid concentrations in the digestive fluid of each test group in Example 3.

[0030] Figure 5 These are the test results of the changes in free ammonia nitrogen concentration in the digestive fluid of each test group in Example 4. DETAILED DESCRIPTION

[0031] The present invention is described in detail below in conjunction with specific implementation methods. The following specific embodiments are helpful for those skilled in the art to further understand the present invention, but do not limit the present invention in any form.

[0032] Example 1: Preparation of modified biochar loaded ball-milled zero-valent iron sulfide

[0033] (1) Weigh 3.6 g of original zero-valent iron and 0.58 g of elemental sulfur and place them in a 304 stainless steel tank containing 5 Φ8 stainless steel beads. Fix the stainless steel tank and set the parameters of the ball mill: forward rotation for 20 min, rest for 2 min, reverse rotation for 20 min, total time for 120 min, and the rotation speed is 500 rpm. After the ball milling is completed, the solid powder obtained is the ball-milled sulfide zero-valent iron, which is placed in a sealed bag purged with high-purity nitrogen in advance and stored for later use, recorded as SZVI.

[0034] (2) 8 g of wheat straw powder was placed in a 500 mL mixed solution of hydrochloric acid and polyethylene glycol (the concentration of polyethylene glycol in the mixed solution was 8.9 g / L), magnetically stirred (speed of 1200 rpm) for 180 min for chemical modification, filtered and placed in an oven at 60 ° C for drying. The modified biochar was placed in a tubular furnace with continuous nitrogen flow, and the heating rate was set to 5 ° C / min; after 120 min, it was heated to 650 ° C, maintained at this temperature for 180 min, and then automatically entered the cooling program, cooled naturally to room temperature, and sealed for storage for later use.

[0035] (3) Under continuous stirring, 0.18 g of modified straw biochar powder and 3.4 g of SZVI were slowly added to a mixed solution of NaBH4 and Na2S2O4 (mass ratio of 6.07:1), and stirring was continued to allow for full reaction. After filtration, washing, and drying, the modified biochar-loaded ball-milled sulfidized zero-valent iron material was obtained, which was recorded as SZVI-BC.

[0036] The modified biochar-loaded ball-milled sulfidized zero-valent iron material SZVI-BC in Example 1 was characterized by scanning electron microscopy. Figure 1 As shown, SZVI is filled on the surface and pores of biochar, which is beneficial to reduce the agglomeration of zero-valent iron sulfide particles and simultaneously changes the charge on the biochar surface.

[0037] Example 2: Study on the daily methane production of thermal hydrolysis coupled with anaerobic digestion of high-solid sludge by ball-milled sulfidized zero-valent iron material loaded with modified biochar

[0038] The anaerobic digestion reactor is a continuous stirring high temperature (56±1)℃, the reactor volume is 1.3 L, and the effective volume is 0.9 L. The hydraulic retention time of the reactor is 2 to 5 days, the organic loading rate is 2.09g / (L d), the operating temperature is set at (56±1)℃, and the stirring rate is set at 110r / min. The sludge matrix is ​​a high-solid content sludge thermal hydrolyzate, and its parameters are: pH = (6.3 ± 0.1), VSS = (32.91 ± 3.07) g / L; TS = (72.82 ± 3.07) g / L; VS = (40.92 ± 2.97) g / L; the inoculated sludge comes from a high-solid content sewage with a solid content of 10% that has been stably operated in the laboratory for more than 80 days, and its parameters are pH = (7.3 ± 0.2), VSS = (6.92 ± 3 = 0.39) g / L; TS = (15.91 ± 3.92) g / L; VS = (5.89 ± 0.62) g / L. The average VS removal rate of the digestion device is 46.7%, and the pH value is 7.69 ± 0.12.

[0039] In this embodiment, five parallel tests were set up, and the dosage of modified biochar loaded with ball-milled sulfide zero-valent iron SZVI-BC in each group was 0, 0.12, 0.24, 0.36, 0.48, and 0.62 g, respectively recorded as the control group, SF(0), SF(1), SF(2), SF(3), and SF(4). During the anaerobic digestion, the reaction device was manually filled with mud and discharged with a syringe every day to ensure the continuous operation of the digestion device. After the digestion device was continuously operated for 36 days, the exhaust was stopped, and the methane content and mud components of each experimental group were tested.

[0040] The test results are as follows Figure 2 As shown. Figure 2 It can be seen that the daily methane production of the test group with modified biochar loaded with ball-milled sulfide zero-valent iron is significantly higher than that of the blank group. For example, the cumulative gas production of the SF3 test group is 1.52 times that of the blank group. However, the amount of modified biochar loaded with ball-milled sulfide zero-valent iron is not necessarily better. The experimental data show that when the dosage continues to increase to 0.62g, the methane production decreases, indicating that the activity of methanogens is inhibited at this time. In the start-up period of high-temperature and high-solid anaerobic digestion of municipal sludge, the optimal dosage is 1.83g / L of modified biochar loaded with ball-milled sulfide zero-valent iron material.

[0041] The increase in methane production is due to the fact that the conductivity of biochar and zero-valent iron can stimulate direct interspecies electron transfer for anabolism. At the same time, zero-valent iron can serve as a direct electron donor for methanogens, accelerating electron transfer. In addition, the combination of sulfided zero-valent iron and biochar can effectively improve its electron acceptance and electron supply capabilities, which is beneficial to the degradation and transformation of organic matter.

[0042] Example 3: Effect of modified biochar loaded with ball-milled sulfidized zero-valent iron material on the degradation and transformation of volatile organic acids (VFAs) in thermal hydrolysis coupled with anaerobic digestion of high-solid sludge

[0043] Acetic acid and propionic acid are the main components of volatile fatty acids (VFAs), accounting for about 78% of the total amount of VFAs. Therefore, the changes in the content of acetic acid and propionic acid can reflect the overall trend of changes in VFAs. Referring to the steps and test methods of Example 2, samples were taken every 3 days during the digestion period to measure the changes in the concentrations of acetic acid and propionic acid in the digestive fluid.

[0044] The test results are as follows Figure 3As shown. The study showed that the acetic acid concentration in each test group first accumulated and then consumed, and reached a peak before the 7th day. During the entire period of high-temperature anaerobic digestion, the rate of decrease of acetic acid concentration in the digestion device with modified biochar-loaded ball-milled sulfide zero-valent iron material was significantly greater than that of the blank group. Among them, the average acetic acid concentration of the SF1, SF2, SF3, and SF4 test groups was 26.03%, 35.23%, 42.28%, and 32.59% lower than that of the blank group without modified biochar-loaded ball-milled sulfide zero-valent iron material.

[0045] The accumulated propionic acid in the anaerobic digestion system affects the metabolic rate relatively slowly and is considered to be the rate-limiting factor for methanogenesis. Moreover, propionic acid can only be converted into acetic acid at a lower redox potential. Figure 4 As shown in the figure, the propionic acid content of the blank group after 11 days of digestion was significantly higher than that of the experimental group with modified biochar loaded ball-milled sulfide zero-valent iron material. The average acetic acid content of the experimental groups with 0.12g, 0.24g, and 0.36g of modified biochar loaded ball-milled sulfide zero-valent iron was reduced by 14.49%, 15.76%, and 20.75% respectively compared with the blank group. This shows that the modified biochar loaded ball-milled sulfide zero-valent iron material helps to accelerate the degradation of propionic acid in the digestion system and alleviate the accumulation of propionic acid. This is because lactic acid modified with sulfide zero-valent iron promotes the production of methane, while optimizing the microbial metabolic pathway and alleviating the inhibition of propionic acid accumulation in the digestion system.

[0046] Example 4: Modified biochar loaded ball-milled sulfidized zero-valent iron material alleviates the volatile ammonia inhibition phenomenon in thermal hydrolysis coupled with anaerobic digestion of high-solid sludge

[0047] Ammonia nitrogen is an important inhibitor of microbial activity during the anaerobic digestion of high-temperature and high-solid sludge. When the ammonia nitrogen concentration in the biogas exceeds 550 mg / L, the digestion rate will be severely inhibited. Referring to the steps and test methods of Example 2, samples were taken every 3 days during the digestion period to measure the changes in the ammonia nitrogen concentration of the digestate. The test results are as follows: Figure 5 As shown. The concentration of TAN in each test group reached its peak on the 22nd to 24th day of digestion, while on the 24th day of digestion, the TAN concentration of the blank group was much higher than the inhibition threshold, indicating that the anaerobic digestion of the blank group was inhibited at this time. During the entire digestion period, the average TAN concentration of the test group with modified biochar loaded with ball-milled sulfidized zero-valent iron material was between 412.39 and 483.78 mg COD / L, which was 31.86% to 41.69% lower than that of the blank group without addition.

[0048] The test results show that modified biochar-loaded ball-milled sulfide zero-valent iron material helps alleviate the ammonia inhibition phenomenon in the digestion system. This is because the porous conductive properties of modified biochar-loaded ball-milled sulfide zero-valent iron material can significantly reduce TAN concentration and alleviate ammonia inhibition, thereby improving the stability of high-temperature and high-solid anaerobic digestion process.

[0049] Example 5: Effects of different S / Fe molar ratios on the biotoxicity of heavy metals in digested sludge

[0050] Weigh 3.5g of the original iron powder in four identical 304 stainless steel tanks, and then add 3 Φ10 stainless steel beads, 5 Φ8 stainless steel beads, 9 Φ5 stainless steel beads and 12 Φ3 stainless steel beads, i.e. R2, R3, R4 and R5 in Table 1, according to different sulfur-iron mass ratios (sulfur-iron mass ratios are 0.12, 0.16, 0.20, and 0.26, respectively). After the four stainless steel tanks are fixed, the ball mill is programmed as follows: forward rotation for 20min, rest for 2min, reverse rotation for 20min, total duration of 120min, and the rotation speed is 500rpm. After the ball milling is completed, the powders in the four stainless steel tanks are respectively placed in sealed bags swept with high-purity nitrogen and stored for standby use. The rest is referred to the steps of Example 1 and Example 2. Samples are taken every 3d during the digestion period to determine the heavy metal content in the digestion fluid sample.

[0051] Table 1 shows the effect of different S / Fe molar ratios on digestion results

[0052]

[0053] The test results are shown in Table 1. Different sulfur-iron mass ratios have a great influence on the content of heavy metals in the digestate. It is necessary to select a modified biochar loaded with sulfide zero-valent iron material with a suitable sulfur-iron mass ratio to have a greater adsorption and complexation effect on the heavy metals in the digestate. Calculations show that the optimal sulfur-iron content ratio is 0.16, at which time the material exhibits the best adsorption and toxicity reduction effect. The principle is that the biochar material modified with sulfide zero-valent iron increases its active sites and surface functional groups, thereby improving the solidification capacity of heavy metals in sludge. The addition of modified biochar materials can reduce the mobility, bioavailability and toxicity of heavy metals after digestion of high-temperature and high-solid sludge, which is beneficial to the resource utilization of sludge.

[0054] Obviously, the above embodiments of the present invention are merely examples to more clearly illustrate the present invention, and are not limitations on the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made on the basis of the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the protection scope of the present invention.

Claims

1. A method for preparing a modified biochar-loaded ball-milled sulfided zero-valent iron material, comprising: (1) ball-milled sulfur and original zero-valent iron are subjected to sulfurization modification to obtain ball-milled sulfurized zero-valent iron; The wheat straw powder is added to a mixed solution of hydrochloric acid and polyethylene glycol, and chemically modified by magnetic stirring, filtered and dried. The obtained powder is placed in a tubular furnace for pyrolysis under anaerobic conditions, and naturally cooled to room temperature to obtain modified straw biochar. (2) Add a mixed solution of NaBH4 and Na2S2O4 to the modified straw biochar and ball-milled zero-valent iron sulfide obtained in step (1), stir to allow for sufficient reaction, and obtain a modified biochar-loaded ball-milled zero-valent iron sulfide material after filtering, washing, and drying.

2. The preparation method according to claim 1, characterized in that: In step (1), the original zero-valent iron and elemental sulfur are weighed and placed in a 304 stainless steel tank filled with Φ8 stainless steel beads. The stainless steel tank is fixed and the parameters of the ball mill are set as follows: forward rotation for 20 to 30 minutes, rest for 2 to 4 minutes, reverse rotation for 20 to 30 minutes, a total time of 120 to 150 minutes, and a rotation speed of 500 to 700 rpm.

3. The preparation method according to claim 1, characterized in that: In step (1), wheat straw powder is added to a mixed solution of hydrochloric acid and polyethylene glycol, and magnetic stirring is performed at a speed of 1200 rpm for 180 minutes for chemical modification, and the mixture is filtered and placed in an oven at 60° C. for drying. The mass volume ratio of the wheat straw powder to the mixed solution of hydrochloric acid and polyethylene glycol is 8:500 g / mL, and the concentration of polyethylene glycol in the mixed solution is 6 to 13 g / L.

4. The preparation method according to claim 3, characterized in that: In step (1), the temperature rise program of pyrolysis is: the temperature rise rate is controlled at 5-8°C / min; after 120 minutes, it is heated to 650°C, and the temperature is maintained for 180 minutes before automatically entering the temperature drop program.

5. The preparation method according to claim 1, characterized in that: In step (2), the mass ratio of NaBH4 and Na2S2O4 in the mixed solution of NaBH4 and Na2S2O4 is 6.07:1; the mass volume ratio of the total mass of the modified straw biochar and ball-milled zero-valent iron sulfide to the mixed solution of NaBH4 and Na2S2O4 is 1:15.6-17.2, and the mass ratio of the modified straw biochar and ball-milled zero-valent iron sulfide is 1:18.9-20.

1.

6. A modified biochar-loaded ball-milled sulfided zero-valent iron material, prepared by the preparation method described in any one of claims 1 to 5.

7. Application of the modified biochar-loaded ball-milled sulfidized zero-valent iron material described in claim 6 in anaerobic digestion of high-temperature and high-solid sludge by thermal hydrolysis.

8. The use according to claim 7, characterized in that: At the initial stage of starting the anaerobic digestion reactor, the modified biochar-loaded ball-milled sulfided zero-valent iron is added to the anaerobic digestion reactor. The hydraulic retention time of the anaerobic digestion reactor is 2 to 5 days, the organic loading rate is 2.09 g / Ld, the operating temperature is set to 56±1°C, and the stirring rate is set to 110 r / min.

9. The use according to claim 8, characterized in that: 4 to 7 days after the anaerobic digestion reactor has been running, the modified biochar loaded with ball-milled sulfided zero-valent iron is added to the anaerobic digestion reactor.

10. The use according to claim 8, characterized in that: The amount of modified biochar loaded with ball-milled sulfidized zero-valent iron was 1.32-2.06 g / L.

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