Preparation method of Fe-C@S porous core-shell structure denitrification filler

Abstract

The present invention discloses a preparation method of a Fe-C@S porous core-shell structure denitrification filler. First, each raw material for preparing the denitrification filler is weighed according to the set content; reduced iron powder, activated carbon powder and binder are mixed evenly; the wetted mixed raw materials are extruded into pellets in a granulator to obtain an internal iron-carbon core; the iron-carbon core is placed in a constant-temperature oven for drying and then cooled at room temperature; the dried and cooled iron-carbon core is placed in a tubular muffle furnace for high-temperature roasting and cooled to room temperature after roasting; the sulfur matrix is heated to a molten state, and then the molten sulfur matrix is wrapped on the surface of the iron-carbon core by the method of dip impregnation to obtain a Fe-C@S porous core-shell structure denitrification filler. The filler prepared according to the above method can maintain the stability of the effluent pH and realize the functions of slow iron release and sulfur cycle through the porous structure, so as to construct a material with low carbon emissions, high-efficiency denitrification and rapid sulfur cycle.

Description

Technical Field

[0001] The present invention relates to the technical field of autotrophic denitrification treatment, and particularly relates to a preparation method of an Fe-C@S porous core-shell structure denitrification filler. Background Art

[0002] The discharge of a large amount of nitrogen into water bodies can cause eutrophication of water bodies, form water blooms and red tides, and damage biodiversity. The nitrate pollution in water bodies can also cause harm to the human body. Therefore, it is necessary to effectively denitrify sewage. Traditional heterotrophic denitrification requires the consumption of organic carbon sources to reduce nitrate. In this process, the organic matter in low C / N sewage is significantly insufficient, thus affecting the denitrification effect of denitrification. To improve the denitrification efficiency, a large amount of carbon source often needs to be added to the sewage. This increases the cost of denitrification and even generates secondary pollution such as a large amount of sludge. To overcome the disadvantages of heterotrophic denitrification, an autotrophic denitrification technology that does not require an external carbon source has been developed. According to different electron donors, autotrophic denitrification technologies mainly include sulfur-based autotrophic denitrification, iron-based autotrophic denitrification, and hydrogen-based autotrophic denitrification. Among them, sulfur-based autotrophic denitrification technology has become a current research hotspot due to its wide application.

[0003] The sulfur-based autotrophic denitrification process is a process in which Thiobacillus denitrificans uses reduced sulfur as an electron donor and NO 3 - as an electron acceptor to reduce NO 3 - to N 2 . This reaction does not require an external organic matter and has a high denitrification efficiency. It is an important technology for denitrifying low-carbon source wastewater. However, a large amount of H + is generated during the sulfur autotrophic denitrification reaction, and sulfur is oxidized to SO 4 2- in this process. Its yield will increase with the increase of NO 3 - -N in the sewage, reducing the denitrification efficiency and affecting the effluent quality. At the same time, a large amount of SO 4 2- is discharged into the environment, and toxic H 2 S may be released due to anaerobic action. It will also corrode pipelines and treatment facilities, damage the soil and make it compact, thus endangering human health and damaging the ecological environment. In the existing field of water purification technology, there is still a lack of a denitrification filler that can maintain the stability of the effluent pH, reduce the content of SO 4 2- in the effluent, has high denitrification efficiency and is environmentally friendly and economical. Therefore, it is necessary to develop an autotrophic denitrification filler with a low SO 4 2- yield. In addition, introducing iron into sulfur autotrophic denitrification can provide multiple electron donors to participate in denitrification. Theoretically, it can overcome SO4 2- Produce the disadvantages of excessive production and insufficient alkalinity. Research shows that SO 4 2- can be reduced to low-valence sulfur by the action of iron-carbon microelectrolysis, and since the generated sulfide ions can form FeS precipitation with iron without generating H 2 S, not only can the harm of SO 4 2- under anaerobic conditions be eliminated, but FeS can also be reused as an electron donor for sulfur autotrophic denitrification. However, simply mixing iron into the filler easily leads to the hardening and rusting of the filler, shortening the service life of the filler and affecting the denitrification efficiency. Therefore, there is an urgent need to develop a denitrification filler that can recycle sulfur and whose filler is not prone to hardening. Summary of the Invention

[0004] The purpose of the present invention is to provide a preparation method of an Fe-C@S porous core-shell structure denitrification filler. The filler prepared according to this method can maintain the stability of the effluent pH and realize the functions of slow release of iron and sulfur cycle through the porous structure, so as to construct a material with low carbon emissions, high-efficiency nitrogen removal, and rapid sulfur cycle.

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

[0006] A preparation method of an Fe-C@S porous core-shell structure denitrification filler, the method comprising:

[0007] Step 1, Weigh each raw material for preparing the denitrification filler according to the set content; wherein, each raw material includes a sulfur matrix, reduced iron powder, activated carbon powder, and a binder;

[0008] Step 2, Mix the reduced iron powder, activated carbon powder, and the binder evenly, and moisten the mixed raw materials with water;

[0009] Step 3, Extrude the moistened mixed raw materials into pellets in a granulator so that the particle size is 3-5 mm to obtain an internal iron-carbon core;

[0010] Step 4, Place the iron-carbon core obtained in Step 3 in a constant-temperature oven to dry and then cool it at room temperature;

[0011] Step 5, Place the dried and cooled iron-carbon core in a tubular muffle furnace with an inert protective gas flowing through it for high-temperature roasting, and cool it to room temperature after the roasting is completed;

[0012] Step 6, Heat the sulfur matrix to a molten state, and then wrap the molten sulfur matrix on the surface of the iron-carbon core treated in Step 5 by the method of dipping and lifting, and cool it to room temperature to obtain an Fe-C@S porous core-shell structure denitrification filler.

[0013] As can be seen from the technical solution provided by the present invention above, the filler prepared according to the above method can maintain the stability of the effluent pH and realize the functions of slow iron release and sulfur cycle through the porous structure, thereby constructing a material with low carbon emissions, efficient denitrification, and rapid sulfur cycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0015] Figure 1 Schematic flow chart of the preparation method of the Fe-C@S porous core-shell structure denitrification filler provided by the embodiment of the present invention;

[0016] Figure 2 Mechanism diagram of the Fe-C@S porous core-shell structure denitrification filler provided by the embodiment of the present invention;

[0017] Figure 3 Schematic diagram of the comparison of denitrification effects between Example 1 and the comparative example provided by the embodiment of the present invention;

[0018] Figure 4 Schematic diagram of the denitrification performance of Example 2 provided by the embodiment of the present invention;

[0019] Figure 5 Schematic diagram of the sulfate reduction performance of Example 2 provided by the embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0020] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments, which does not constitute a limitation to the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the protection scope of the present invention.

[0021] As Figure 1 shown is the schematic flow chart of the preparation method of the Fe-C@S porous core-shell structure denitrification filler provided by the embodiment of the present invention, and the method includes:

[0022] Step 1: Weigh each raw material for preparing the denitrification filler according to the set content;

[0023] Among them, each raw material includes a sulfur matrix, reduced iron powder, activated carbon powder, and a binder;

[0024] In this step, the set content is specifically as follows:

[0025] By weight, the content of each raw material component is: 50 - 80 parts of sulfur matrix; 15 - 45 parts of reduced iron powder; 10 - 22 parts of activated carbon powder; 5 - 35 parts of binder.

[0026] In specific implementation, the sulfur matrix is specifically sublimed sulfur. Elemental sulfur has low biological toxicity, high sulfur component content, low cost, is easy to store and transport, and is insoluble in water.

[0027] The reduced iron powder is specifically one or both of nano zero-valent iron and particulate zero-valent iron. It has a low price and strong reducibility, and can improve the denitrification performance.

[0028] The activated carbon powder has the advantages of good adsorption performance, strong decolorization and odor removal ability, being economical and durable, etc. It can be in full contact with the reduced iron powder to form a large number of primary batteries, enhancing the reduction rate.

[0029] The binder is one or more of diatomite, kaolin clay and carboxymethyl cellulose. Among them, diatomite has the advantages of porosity, low density, large specific surface area and high chemical stability, etc.; kaolin clay has good adsorption and can adsorb nitrogen and phosphorus pollutants; carboxymethyl cellulose is a relatively common binder, with strong hygroscopicity, being easily soluble in water and showing high viscosity.

[0030] Here, the addition of the sulfur matrix can provide an electron donor for autotrophic denitrifying microorganisms to increase microbial activity and enhance the denitrification effect. And by wrapping the molten sulfur matrix on the surface of the iron-carbon spheres, a porous structure is formed as the S-Fe-N migration channel; the binder can enhance the strength of the filler, and the filler is not easy to loosen, prolonging the service life of the filler; the addition of reduced iron increases an additional electron donor and the iron autotrophic process consumes H + , maintaining the pH stability in the system; the addition of activated carbon can form a primary battery with the reduced iron to reduce SO produced during the sulfur autotrophic denitrification process 4 2- . Therefore, the filler has the functional characteristics of stabilizing its own pH, forming a sulfur cycle and slow release of iron during the denitrification process.

[0031] Step 2: Mix the reduced iron powder, activated carbon powder and binder evenly, and moisten the mixed raw materials with water;

[0032] Step 3: Extrude the moistened mixed raw materials into pellets in a granulator, so that the particle size is 3 - 5 mm to obtain an internal iron-carbon core;

[0033] Step 4: After drying the iron-carbon core obtained in Step 3 in a constant-temperature oven, cool it at room temperature;

[0034] In this step, the drying time in the oven is generally 120 min.

[0035] Step 5: Place the dried and cooled iron-carbon core in a tubular muffle furnace filled with inert protective gas for high-temperature roasting, and cool it to room temperature after the roasting is completed;

[0036] In this step, the high-temperature roasting temperature in the tubular muffle furnace is set at 800 °C, and the roasting time is set at 120 min.

[0037] Step 6: Heat the sulfur matrix to the molten state, and then wrap the molten sulfur matrix on the surface of the iron-carbon core processed in Step 5 by the method of dip impregnation, and cool it to room temperature to obtain the Fe-C@S porous core-shell structured denitrification filler.

[0038] As Figure 2 shown in the mechanism diagram of the Fe-C@S porous core-shell structured denitrification filler provided by the embodiment of the present invention, it can be seen from Figure 2 that: the external sulfur shell provides the electron donor required for sulfur autotrophic denitrification, and performs iron autotrophic denitrification in the way of slow-release iron. The acid consumption in this process can be used as a supplement to alkalinity to maintain the pH stability during the denitrification process. At the same time, it can reduce the direct contact between iron and sewage, avoid the packing from caking, and create a good autotrophic denitrification environment; while the iron and carbon in the inner core can form a primary battery, and [H] and Fe generated on the surface of Fe under the action of microcurrent 2+ , has strong reducing ability, can reduce sulfate in water to low-valent sulfur, and continuously provide electron donors for sulfur autotrophy. Therefore, the Fe-C@S porous core-shell structured denitrification filler is a sulfur autotrophic-iron-carbon microelectrolysis synergistic denitrification material with sulfur cycle function.

[0039] It should be noted that the content not described in detail in the embodiment of the present invention belongs to the prior art well-known to those skilled in the art.

[0040] The filler prepared by the method according to the above embodiment can maintain the stable pH of the effluent, efficiently denitrify and has a sulfur cycle function. The denitrification effect of the prepared filler is illustrated by specific examples as follows:

[0041] Example 1: Raw materials used: 50-80 parts of sublimed sulfur, 15-45 parts (100 mesh) of reduced iron powder, 10-22 parts (200 mesh) of activated carbon powder, 5-35 parts of binder, and the binder is one or more of diatomite, kaolin clay and carboxymethyl cellulose.

[0042] The preparation process is as follows:

[0043] Step 1: Weigh each raw material for preparing the novel denitrification filler according to the set content;

[0044] Step 2: Mix each raw material evenly, and moisten the mixed raw materials with water;

[0045] Step 3: Extrude the wetted mixed raw materials into pellets in a granulator, with the particle size being 3 - 5 mm, to obtain an internal iron-carbon core;

[0046] Step 4: Place the iron-carbon core in a constant-temperature oven and dry it for 120 min, then cool it to room temperature;

[0047] Step 5: Place the dried iron-carbon core in a tubular muffle furnace filled with an inert protective gas, calcine it at 800 °C for 120 min, and then cool it to room temperature;

[0048] Step 6: Heat the sulfur matrix to 120 °C. After the sulfur matrix melts into a liquid state, coat the surface of the prepared iron-carbon core with the sulfur matrix by the method of dip impregnation, and then cool it to room temperature to obtain a novel Fe-C@S porous core-shell structured denitrification filler.

[0049] Comparative Example 1: A sulfur autotrophic denitrification filler 1 in the prior art

[0050] Raw materials used in Comparative Example 1: 200 g of sublimed sulfur and 60 g of kaolin clay (100 mesh).

[0051] Preparation method:

[0052] Step 1: Weigh each raw material for preparing the filler according to the set content;

[0053] Step 2: Mix the raw materials evenly and moisten the mixed raw materials with water;

[0054] Step 3: Extrude the wetted mixed raw materials into pellets in a granulator, with the particle size being 3 - 5 mm;

[0055] Step 4: Place the wetted filler in a constant-temperature oven and dry it for 120 min, then cool it to room temperature to obtain the sulfur autotrophic denitrification filler 1.

[0056] Comparative Example 2: A sulfur autotrophic denitrification filler 2 in the prior art

[0057] Raw materials used in Comparative Example 2: 200 g of sulfur paste and 60 g of kaolin clay (100 mesh). Among them, the sulfur paste in the raw materials comes from the sulfur-based product after biogas desulfurization, with a sulfur content of more than 97.5%.

[0058] Preparation method:

[0059] Step 1: Weigh each raw material for preparing the filler according to the set content;

[0060] Step 2: Mix the raw materials evenly and moisten the mixed raw materials with water;

[0061] Step 3: Extrude the wetted mixed raw materials into pellets in a granulator, with the particle size being 3 - 5 mm;

[0062] Step 4: Place the moist filler in a constant-temperature oven and dry it for 120 min, then cool it to room temperature to obtain the sulfur autotrophic denitrification filler 2.

[0063] Then, place the fillers obtained in Example 1, Comparative Example 1, and Comparative Example 2 in conical flasks respectively. Use artificial simulated wastewater as the experimental wastewater, with an influent nitrate nitrogen of 30 mg / L and phosphate of 10 mg / L. Take the anaerobic pond sludge from a certain landfill leachate treatment plant as the inoculated sludge, and conduct an inoculation and acclimation shaker experiment with simulated wastewater plus an equal amount of sludge as the blank control. Take water samples at the same interval to detect indicators such as nitrate nitrogen, nitrite nitrogen, sulfate radical, and pH to explore the denitrification characteristics of the filler.

[0064] As Figure 3 shown is the schematic diagram of the denitrification effect comparison between the examples and comparative examples provided in the embodiments of the present invention. Combining Figure 3 it can be seen that after 5 h of the acclimation stage with the addition of sludge, the nitrate nitrogen begins to decline, indicating successful acclimation and entry into the reaction stage. In Comparative Examples 1 and 2, the degradation rate of nitrate nitrogen is relatively fast, and the nitrate nitrogen is completely degraded in about 15 h, but there is accumulation of nitrite nitrogen and a large amount of sulfate radical to varying degrees. While the reaction time of Example 1 of the present invention is 20 - 25 h. This may be because the water solubility of molten sulfur is poor and it takes a longer time to be utilized by microorganisms. However, in Example 1, there is less accumulation of nitrite nitrogen during the degradation of nitrate nitrogen, and there is no increase in sulfate radical throughout the process, that is, almost all the sulfate radicals generated during the sulfur autotrophic denitrification process in Example 1 are reduced.

[0065] Example 2: The raw materials used in this example are: 50 - 80 parts of sublimed sulfur, 15 - 45 parts of reduced iron powder (100 mesh), 10 - 22 parts of activated carbon powder (200 mesh), and 5 - 35 parts of binder. The binder is one or more of diatomaceous earth, kaolin clay, and carboxymethyl cellulose.

[0066] Preparation process: The same as Example 1.

[0067] Then, place the filler obtained in Example 2 in a conical flask, and use actual landfill leachate as the experimental wastewater, with an influent nitrate nitrogen of 100 mg / L, nitrite nitrogen of 0.04 - 0.1 mg / L, ammonia nitrogen of 0.05 - 1.0 mg / L, and sulfate radical of 80 mg / L. Take the anaerobic pond sludge from a certain landfill leachate treatment plant as the inoculated sludge for the denitrification experiment. Take water samples at the same interval to detect indicators such as nitrate nitrogen, nitrite nitrogen, sulfate radical, and pH to explore the denitrification characteristics and sulfur cycle characteristics of the filler.

[0068] As Figure 4 shown is the schematic diagram of the denitrification performance of Example 2 provided in the embodiments of the present invention. As Figure 5 shown is the schematic diagram of the sulfate radical reduction performance of Example 2. Combining Figure 4 and5 It can be seen that the best effect is achieved under the conditions of 30 °C and an influent pH of 8 for 8 h. The removal rate of TN is above 95%, the effluent pH is between 6 and 8, and the sulfate radical is between 550 and 700 mg / L. At a longer reaction time (30 h), the filler prepared in the embodiment of the present invention can not only reduce the sulfate radical generated in the sulfur autotrophic denitrification process during the sulfur autotrophic process, but also reduce the original sulfate radical in the sewage. The removal rate of the original sulfate radical in the influent is 83%, indicating that the rate of sulfate radical reduction by the filler described in the embodiment of the present invention is greater than the rate of sulfate radical generation during the sulfur autotrophic process. Therefore, it can be concluded that the filler described in the embodiment of the present invention has a good reduction effect on sulfate radicals and has the ability of sulfur cycling.

[0069] In summary, the method described in the embodiment of the present invention has the following advantages:

[0070] 1. It has the function of self-stabilizing pH: Compared with the traditional sulfur autotrophic denitrification filler, the Fe-C@S porous core-shell structure denitrification filler prepared by the method of the present invention, due to the addition of reduced iron, provides an additional electron donor, reduces the burden of sulfur source, and at the same time has the effect of stabilizing pH.

[0071] 2. Fast sulfur cycling: Theoretically, traditional sulfur autotrophic denitrification filler uses elemental sulfur to reduce 1 g of NO 3 - -N, which will produce 7.54 g of SO 4 2- , and it has been experimentally proved that the Fe-C@S porous core-shell structure denitrification filler prepared by the method of the present invention, due to the galvanic cell effect of iron-carbon microelectrolysis, can reduce the SO 4 2- produced by sulfur autotrophic denitrification, and the reduced sulfur can still provide an electron donor for sulfur autotrophic denitrification, promoting the sulfur cycling function of the filler.

[0072] 3. Slow release of iron reduces caking: The Fe-C@S porous core-shell structure denitrification filler prepared by the method of the present invention utilizes its own porous structure, enabling zero-valent iron and divalent iron in the internal iron-carbon core to slowly release into the wastewater. While providing an iron autotrophic electron donor, it reduces the contact between iron and the wastewater, reduces the caking rate, and improves the service life of the filler.

[0073] As described above, it is only the preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims. The information disclosed in the background art part of this article is only intended to deepen the understanding of the overall background technology of the present invention, and should not be regarded as an admission or any form of implication that this information constitutes the prior art known to those skilled in the art.

Claims

1. A method for preparing a Fe-C@S porous core-shell structure denitrification filler, characterized in that: The method comprises: Step 1, weighing various raw materials for preparing denitrification filler according to the set content; wherein the raw materials include sulfur matrix, reduced iron powder, activated carbon powder and adhesive; Step 2, mixing the reduced iron powder, activated carbon powder and binder evenly, and moistening the mixed raw materials with water; Step 3, extruding the wetted mixed raw materials into granules in a granulator to obtain a granule size of 3 to 5 mm to obtain an internal iron-carbon core; Step 4, drying the iron-carbon core obtained in step 3 in a constant temperature oven, and then cooling at room temperature; Step 5, placing the dried and cooled iron-carbon core in a tubular muffle furnace with an inert protective gas for high-temperature roasting, and cooling to room temperature after roasting; Step 6: heat the sulfur matrix to a molten state, and then wrap the molten sulfur matrix onto the surface of the iron-carbon core treated in step 5 by a pulling and impregnation method, and cool to room temperature to obtain a Fe-C@S porous core-shell structure denitrification filler.

2. The method for preparing the Fe-C@S porous core-shell structure denitrification filler according to claim 1, characterized in that: In step 1, the content is set as follows: Calculated by weight, the content of each raw material component is: 50-80 parts of sulfur matrix; 15-45 parts of reduced iron powder; 10-22 parts of activated carbon powder; 5-35 parts of adhesive.

3. The method for preparing the Fe-C@S porous core-shell structure denitrification filler according to claim 1, characterized in that: In step 1, the sulfur matrix is ​​specifically sublimated sulfur.

4. The method for preparing the Fe-C@S porous core-shell structure denitrification filler according to claim 1, characterized in that: In step 1, the reduced iron powder is specifically nano zero-valent iron.

5. The method for preparing the Fe-C@S porous core-shell structure denitrification filler according to claim 1, characterized in that: In step 1, the reduced iron powder is specifically granular zero-valent iron.

6. The method for preparing the Fe-C@S porous core-shell structure denitrification filler according to claim 1, characterized in that: In step 1, the binder is one or more of diatomaceous earth, kaolin clay and carboxymethyl cellulose.

7. The method for preparing the Fe-C@S porous core-shell structure denitrification filler according to claim 1, characterized in that: In step 5, the temperature of high temperature calcination in the tubular muffle furnace is set to 800° C., and the calcination time is set to 120 min.

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