System and method for removing hydrogen sulfide and increasing biogas generation using iron salts and biochar

Abstract

Disclosed are a system and method for removing hydrogen sulfide and increasing biogas generation using iron salts and biochar. The disclosed system for removing hydrogen sulfide and increasing biogas generation using iron salts and biochar comprises: an anaerobic digestion tank that receives organic waste resources and performs anaerobic digestion of the organic waste resources by using anaerobic microorganisms; and an iron salt-biochar supply device that selectively supplies only one of iron salts and biochar or supplies both iron salts and biochar to the anaerobic digestion tank to reduce the concentration of hydrogen sulfide in biogas generated in the anaerobic digestion tank and increase the amount of biogas generated.

Description

System and method for hydrogen sulfide removal and biogas generation enhancement using iron salts and biochar

[0001] The present invention relates to a system and method for removing hydrogen sulfide and increasing biogas generation, and more specifically, to a system and method for removing hydrogen sulfide and increasing biogas generation using iron salt and biochar, which can reduce the amount of hydrogen sulfide generated in an anaerobic digester using high-concentration organic waste, such as in integrated biogasification plants, food waste treatment plants, and livestock wastewater treatment plants, and can increase biogas generation by injecting biochar produced using iron salt and biomass to promote digestion efficiency and induce stabilization, as well as a stable and economical system and method for removing hydrogen sulfide and increasing biogas generation using iron salt and biochar, by utilizing biochar that has chemical reaction by chemicals and microbial immobilization functions.

[0002]

[0003] Generally, the amount of organic waste resources generated, including sewage sludge, is highest for livestock manure at over 85%, followed by food waste at 8% and sewage sludge at about 6.5%, and is steadily increasing.

[0004] Anaerobic digestion methods for the production and use of biogas using such organic waste resources are recognized as the optimal method for achieving carbon neutrality, as well as for promoting recycling in a way that reduces environmental burden and increases social utility.

[0005] Recently, a bill to promote the production and utilization of biogas using organic waste resources has been proposed. This allows for the simultaneous treatment (reduction) of organic waste and the production of biogas, contributing to the production of renewable energy and increasing the energy self-sufficiency of treatment facilities.

[0006] Conventionally, there are various technologies aimed at increasing the digestion efficiency of digesters, and these technologies are described as follows.

[0007] First, as a pretreatment technology, physical and mechanical pretreatments that crush and utilize organic waste, such as microwave irradiation, are used to increase the digestion efficiency of anaerobic microorganisms, but this method has the disadvantage of being complex and difficult to maintain.

[0008] Second, there is a method to increase digestion efficiency and biogas generation by maintaining an appropriate C / N ratio through diversifying and mixing the composition of feed materials, such as the mixed injection of livestock wastewater and food waste; however, since the technology has not yet been fully established, it is technically insufficient for practical application.

[0009] Third, there are methods to introduce specific microbial strains or adjust the operating conditions of anaerobic digesters to maintain microbial diversity, but there are still difficulties in responding effectively due to various condition changes depending on the characteristics of the influent.

[0010] Fourth, there is an external injection method that removes hydrogen sulfide through the reaction of metal ions by injecting chemicals such as iron salts. Although it is applied in a small number of sites with simple additional equipment, there were difficulties such as corrosion of internal equipment due to unestablished operating conditions.

[0011] As mentioned above, there are various types of technologies aimed at improving the efficiency of anaerobic digestion, but these technologies focus on pretreatment methods, and various pretreatment methods are being proposed.

[0012] Specifically, conventional pretreatment methods to improve the efficiency of anaerobic digestion include physical pretreatment, chemical pretreatment, thermal pretreatment, and biological pretreatment methods.

[0013] Physical pretreatment can increase the surface area and improve the contact and decomposition efficiency with microorganisms by breaking down organic matter into smaller pieces using grinding, mechanical destruction, or crushing methods on incoming organic waste. However, since this method is carried out through various process configurations, it requires high energy consumption, as well as installation costs and a large land area due to the multi-stage facility configuration.

[0014] Chemical pretreatment can increase biogas production and improve sludge reduction by pre-decomposing and dissolving influent organic waste under chemical (acidic, alkaline, etc.) conditions to break down its complex and difficult-to-decompose structure, and then supplying it to a digester. However, this method requires the supply of high concentrations of chemicals and a neutralization process, and necessitates separate measures such as operator safety management due to hazardous chemicals.

[0015] Thermal pretreatment can increase biogas production and digestion rate by heating organic waste, such as sludge, to break down cell structures and release internally bound water, which is then supplied to an anaerobic digester. However, safety precautions must be taken due to the high energy requirements for thermal destruction and the risk of forming non-biodegradable compounds.

[0016] Biological pretreatment allows for the supply of pretreatment under environmentally friendly and mild conditions by culturing specific enzymes or microorganisms, but it has the disadvantage of long treatment times and high dependence on the activity of specific microorganisms.

[0017] Although various conventional pretreatment methods are applied to increase biogas production by enhancing anaerobic digestion efficiency, they are not economically viable alternatives due to their decomposition limitations and the sensitivity of various anaerobic microorganisms to growth conditions. To mitigate these limitations, it is essential to optimize the selection of pretreatment based on feedstock and system requirements.

[0018]

[0019] <Prior Art Literature>

[0020] (Patent Document 1) Registered Patent No. 10-1478024

[0021] (Patent Document 2) Registered Patent No. 10-2010124

[0022] (Patent Document 3) Registered Patent No. 10-1309422

[0023]

[0024] The present invention was devised to solve the aforementioned conventional problems, and aims to provide a system and method capable of increasing the amount of biogas produced by reducing the amount of hydrogen sulfide generated in the digester and promoting digestion efficiency by injecting iron salt and biochar into the anaerobic digester.

[0025] In addition, the present invention aims to provide a system and method capable of increasing biogas production and ensuring operational stability of the digester by configuring a facility capable of supplying a mixture of iron salt and biochar, and supplying a certain amount to the anaerobic digester.

[0026]

[0027] The hydrogen sulfide removal and biogas generation enhancement system using iron salt and biochar according to the present invention for achieving the above-mentioned purpose comprises: an anaerobic digester that receives organic waste resources and performs anaerobic digestion of the organic waste resources by anaerobic microorganisms; and an iron salt-biochar supply device that selectively supplies only one of the iron salt or biochar to the anaerobic digester, or supplies both the iron salt and biochar, thereby reducing the concentration of hydrogen sulfide in the biogas generated in the anaerobic digester and increasing the amount of biogas generated.

[0028] The above iron salt-biochar supply device may be configured to reduce the concentration of hydrogen sulfide in biogas by introducing an iron salt composed of either the ferrous chloride series or the ferric chloride series into the upper part of the anaerobic digester to react with the hydrogen sulfide generated during the organic matter decomposition process.

[0029] The above iron salt-biochar supply device can be configured to supply biochar produced based on sewage sludge to the above anaerobic digester to increase the organic matter decomposition efficiency by promoting the growth of anaerobic microorganisms through the porosity of the biochar and adsorbing obstructing substances, thereby improving the production of biogas.

[0030] In addition, the method for removing hydrogen sulfide and increasing biogas generation using iron salt and biochar according to the present invention comprises: a) a step in which organic waste resources are supplied to an anaerobic digester and anaerobic digestion proceeds; and b) a step in which an iron salt-biochar supply device selectively supplies only one of iron salt or biochar to the anaerobic digester, or supplies both iron salt and biochar, thereby reducing the concentration of hydrogen sulfide in the biogas generated in the anaerobic digester and increasing the amount of biogas generated.

[0031] Step b) above may be configured to reduce the concentration of hydrogen sulfide in biogas by introducing an iron salt consisting of either the ferrous chloride series or the ferric chloride series into the upper part of the anaerobic digester to react with the hydrogen sulfide generated during the organic matter decomposition process.

[0032] Step b) above can be configured to improve biogas production by supplying biochar produced based on sewage sludge to the anaerobic digester to increase the organic matter decomposition efficiency through the promotion of anaerobic microbial growth via the porosity of the biochar and the adsorption of obstructing substances.

[0033]

[0034] According to the above, the present invention has the effect of suppressing the generation of hydrogen sulfide during the digestion process of an anaerobic digester using an iron salt, which is an inorganic coagulant, thereby reducing corrosion of purification facilities for biogas utilization and reducing maintenance costs.

[0035] In addition, the present invention has the effect of increasing methane yield by increasing the amount of methane produced by suppressing sulfur that inhibits the growth of anaerobic microorganisms.

[0036] In addition, the present invention has the effect of ensuring more stable operation of the anaerobic digester by injecting biochar having a high surface area and various functional groups into the anaerobic digester so that the functions of the biochar are performed.

[0037] In addition, the present invention can achieve higher organic matter decomposition efficiency by maintaining stabilized microbial activity, and thereby has the effect of significantly increasing biogas production by more than 10%.

[0038] In addition, the present invention can increase the reduction of organic matter by increasing the organic matter decomposition efficiency through the activity of anaerobic microorganisms, thereby having the effect of reducing the operating costs of the treatment plant.

[0039]

[0040] FIG. 1 is a schematic diagram of a system for removing hydrogen sulfide and increasing biogas generation using iron salt and biochar according to one embodiment of the present invention, and

[0041] Figure 2 is a schematic diagram of the experimental apparatus, and

[0042] Figure 3 is a graph comparing the amount of biogas generated with and without the addition of biochar, and

[0043] Figure 4 is a graph comparing the amount of biogas produced according to the amount of biochar injected.

[0044]

[0045] The above objects, other objects, features, and advantages of the present invention will be easily understood through the following preferred embodiments associated with the accompanying drawings. However, the present invention is not limited to the embodiments described herein and may be embodied in other forms. Rather, the embodiments introduced herein are provided to ensure that the disclosed content is thorough and complete, and to ensure that the spirit of the present invention is sufficiently conveyed to those skilled in the art.

[0046] In describing the specific embodiments below, various specific details have been included to explain the invention more concretely and to aid understanding. However, a reader with sufficient knowledge in the art to understand the invention will recognize that it can be used without these various specific details. In some cases, it is noted in advance that commonly known aspects that are not significantly related to the invention have been omitted to prevent unnecessary confusion in describing the invention.

[0047] Hereinafter, with reference to FIGS. 1 to 4, a system and method for removing hydrogen sulfide and increasing biogas generation using iron salt and biochar according to an embodiment of the present invention will be described.

[0048] The hydrogen sulfide removal and biogas generation enhancement system of the present invention is configured to include an anaerobic digester (10) and an iron salt-biochar supply device (20).

[0049] The anaerobic digester (10) is a conventional anaerobic digester that digests organic waste resources by mixing organic waste resources with anaerobic microorganisms and anaerobicating them.

[0050] Organic waste resources such as food waste and livestock wastewater can be separated from impurities and non-organic substances through a pretreatment process and then transferred to an anaerobic digester (10) by means of a pump or other transfer equipment.

[0051] Organic waste resources transferred to the anaerobic digester (10) remain in the anaerobic digester for 20 to 30 days and are mixed with anaerobic microorganisms, and anaerobic conditions are maintained.

[0052] The iron salt-biochar supply device (20) is configured to supply iron salt and / or biochar to the anaerobic digester (10).

[0053] The iron salt-biochar supply device (20) may include an iron salt storage tank and a biochar storage tank that independently store iron salt and biochar, and a transfer device that transfers and supplies the iron salt and biochar stored in the iron salt storage tank and the biochar storage tank to an anaerobic digester (10).

[0054] At this time, the iron salt-biochar supply device (20) may be configured to inject only one of the iron salt and biochar into the anaerobic digester (10), or to inject both the iron salt and biochar into the anaerobic digester sequentially or simultaneously.

[0055] The iron salt-biochar supply device (20) first introduces iron salts of the ferrous chloride (FeCl2) and ferric chloride (FeCl3) series into the upper part of the anaerobic digester (10) to react with hydrogen sulfide generated during the organic matter decomposition process to form insoluble iron sulfide (FeS), thereby reducing the concentration of hydrogen sulfide in the biogas.

[0056] The principle of removing hydrogen sulfide in an anaerobic digester (10) is as follows.

[0057]

[0058] *2FeCl3 + 3H2S → S + 2FeS + 6HCl

[0059] FeCl2 + H2S → FeS + 2HCl

[0060] The optimal amount of iron salt to be injected may vary depending on the H2S concentration and the digester capacity.

[0061] It is recommended to inject Fe and S in a molar ratio of 1:1 to 1.5:1, and excessive application of iron salts can increase costs and potentially interfere with the microbial activity of the digester.

[0062] In addition, the iron salt-biochar supply device (20) is configured to increase the operational stability and biogas production of the anaerobic digester by injecting biochar with porosity and various functionalities into the anaerobic digester (10).

[0063] That is, by supplying biochar to the anaerobic digester (10), the efficiency of organic matter decomposition can be increased through the promotion of anaerobic microbial growth through the porosity of the biochar and the stabilization of operation through the adsorption of obstructing substances.

[0064] In the present invention, the biochar supplied to the anaerobic digester (10) may consist of biochar manufactured based on sewage sludge.

[0065] Sewage sludge-based biochar is produced by pyrolyzing sewage sludge while flowing nitrogen gas under conditions of 400 to 600°C for 1 hour 50 minutes to 2 hours 10 minutes.

[0066] During the production of biochar, the pyrolysis temperature directly affects the carbon content, porosity, and specific surface area of ​​the biochar. Higher temperatures increase the carbon content, producing biochar that is more stable and resistant to microbial degradation. Additionally, higher temperatures tend to result in biochar with a larger surface area and microporous structure, which enhances the adsorption capacity for pollutants such as heavy metals and organic contaminants.

[0067] The sewage sludge-based biochar applied in the present invention is manufactured by pyrolyzing sewage sludge under conditions of 400 to 600°C, and has good resistance to microbial decomposition and excellent adsorption of pollutants due to its large surface area and porosity.

[0068] When the pyrolysis temperature is below 400℃, the sewage sludge is not completely carbonized and remains in a less carbonized state, which degrades the performance of the biochar. When the temperature exceeds 600℃, there is a problem of reduced economic efficiency due to increased fuel consumption for generating thermal energy.

[0069] The biochar introduced into the anaerobic digester (10) performs the following functions.

[0070] First, due to the characteristics of biochar, which has porosity and multiple function groups, it buffers the pH drop caused by organic acids generated during the decomposition of organic matter, thereby increasing microbial activity (pH buffering).

[0071] Second, the large surface area of ​​the injected biochar provides a habitat for microbial communities, enhancing the activity of anaerobic microorganisms and enabling the provision of a stable habitat (immobilization).

[0072] Third, biochar can directly increase energy recovery by acting as an electron acceptor to promote synthetic metabolism among microorganisms, thereby improving the rate of methane production (electron transfer).

[0073] Fourth, biochar enables the stable operation of anaerobic digesters and increases the organic matter decomposition efficiency by adsorbing inhibitory substances such as ammonia and heavy metals that can have an inhibitory effect on microbial activity (adsorption of inhibitory substances).

[0074] As such, the present invention can increase decomposition efficiency by mixing and injecting iron salt and biochar according to the operating site conditions in an anaerobic digester operating facility, and in some cases, each process can be configured separately for application.

[0075] Although the present invention can be effective for removing hydrogen sulfide and increasing biogas production by injecting either iron salt or biochar alone, when iron salt and biochar are injected simultaneously, the iron salt acts as an electron acceptor and precipitates sulfides (e.g., H2S) to reduce the inhibition of methane-producing microorganisms, and the biochar provides a large surface area and promotes microbial community formation to stabilize the microbial ecosystem and also acts as a buffer to increase pH stability and promote electron transfer between microorganisms, making it more effective for removing hydrogen sulfide and increasing biogas production.

[0076] <Experimental Example>

[0077] Experiment 1 - Experiment on Biogas Production with and without Biochar

[0078] To measure the biogas (methane gas) production of biochar produced from sewage sludge, the gas layer from the anaerobic reactor was collected and analyzed after 21 days of reaction (see Fig. 2).

[0079] As shown in Figure 3, experimental results confirmed that when biochar was added to the anaerobic digester, the production yield of biogas (methane gas) increased by 38% compared to when biochar was not added.

[0080] This demonstrates the potential of sewage sludge biochar as a biogas booster.

[0081] Experiment 2 - Experiment on Biogas Production According to Biochar Injection Amount

[0082] To measure the biogas production according to the injection amount of sewage sludge-based biochar produced under conditions of 550℃, the biochar injection amount into the anaerobic digester was varied to 0g / L, 1g / L, and 10g / L, and the gas layer of the anaerobic digester was collected and analyzed after the reaction.

[0083] As a result of the experiment, as shown in Figure 4, it was confirmed that biogas production increased by 6.8% when 1 g / L of biochar was injected.

[0084] In this invention, depending on the operating conditions of the anaerobic digester (10), only iron salt may be supplied to the anaerobic digester (10) through the iron salt-biochar supply device (20), or only biochar may be supplied, and in some cases, both iron salt and biochar may be supplied to achieve stabilization of the anaerobic digester and increased biogas production.

[0085] Although the present invention has been illustrated and described above in relation to preferred embodiments to illustrate the principles of the invention, the invention is not limited to the configuration and operation as illustrated and described. Rather, those skilled in the art will understand that numerous changes and modifications to the invention are possible without departing from the spirit and scope of the appended claims. Accordingly, all such appropriate changes, modifications, and equivalents should be considered to be within the scope of the invention.

[0086]

[0087] The present invention as described above can be widely used in industrial fields related to biogas production.

Claims

1. An anaerobic digester (10) that receives organic waste resources and performs anaerobic digestion of organic waste resources by anaerobic microorganisms; and, A system for removing hydrogen sulfide and increasing biogas generation using iron salt and biochar, characterized by including an iron salt-biochar supply device (20) that selectively supplies only one iron salt or biochar to the anaerobic digester (10), or supplies both iron salt and biochar to reduce the concentration of hydrogen sulfide in the biogas generated in the anaerobic digester (10) and increase the amount of biogas generated.

2. In Paragraph 1, The above iron salt-biochar supply device (20) is configured to introduce an iron salt composed of either a ferrous chloride series or a ferric chloride series into the upper part of the anaerobic digester to react with the hydrogen sulfide generated during the organic matter decomposition process, thereby reducing the concentration of hydrogen sulfide in the biogas. This describes a system for removing hydrogen sulfide and increasing biogas generation using iron salt and biochar.

3. In Paragraph 1, The above iron salt-biochar supply device (20) is configured to supply biochar manufactured based on sewage sludge to the above anaerobic digester (10) to increase the organic matter decomposition efficiency through the promotion of anaerobic microbial growth through the porosity of the biochar and the adsorption of obstructing substances, thereby improving the production of biogas. This describes a system for removing hydrogen sulfide and increasing biogas generation using iron salt and biochar. 4.a) A step in which organic waste resources are supplied to an anaerobic digester (10) and anaerobic digestion proceeds; and, b) a step in which an iron salt-biochar supply device (20) selectively supplies only one iron salt or biochar to an anaerobic digester (10), or supplies both iron salt and biochar to reduce the concentration of hydrogen sulfide in the biogas produced in the anaerobic digester (10) and increase the amount of biogas produced; characterized by including a method for removing hydrogen sulfide and increasing biogas production using iron salt and biochar.

5. In Paragraph 4, The above step b) is characterized by being configured to introduce an iron salt, which is composed of either a ferrous chloride series or a ferric chloride series, into the upper part of the anaerobic digester (10) to react with the hydrogen sulfide generated during the organic matter decomposition process, thereby reducing the concentration of hydrogen sulfide in the biogas. This describes a method for removing hydrogen sulfide and increasing biogas generation using iron salt and biochar.

6. In Paragraph 4, The above step b) is characterized by being configured to supply biochar manufactured based on sewage sludge to the anaerobic digester (10) to increase the organic matter decomposition efficiency through the promotion of anaerobic microbial growth via the porosity of the biochar and the adsorption of obstructing substances, thereby improving the production of biogas. This describes a method for removing hydrogen sulfide and increasing biogas generation using iron salt and biochar.

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