Sulfur-based composite filler and preparation method thereof

Abstract

The invention discloses a sulfur-based composite filler and a preparation method thereof. The sulfur-based composite filler comprises sulfur, an alkaline material, an adhesive and a pore forming agent, the preparation method comprises the following steps: grinding sulfur, an alkaline material, an adhesive and a pore-forming agent into powder, uniformly mixing, preparing the ground raw materials into particles by using a granulator, heating and drying the particles, heating the dried particles at 112-165 DEG C for 10-180 minutes until sulfur on the surfaces of the particles is molten, cooling to room temperature, and shaping to obtain the sulfur-based porous material. The filler forms particles with high hardness, the dissolution rate of the filler in water is reduced, it is guaranteed that the interior of the particles has large porosity, more microbial agents can be loaded, nitrate in wastewater can be efficiently and rapidly removed, the filler prepared through the method has high alkalinity, the addition of alkalinity can be reduced when the filler is applied to sewage treatment, and the service life of the filler is prolonged. The operation cost is reduced.

Description

Technical Field

[0001] The present application relates to the technical field of sewage treatment, and in particular to a sulfur-based composite filler and a method for preparing the sulfur-based composite filler. Background Art

[0002] Sulfur autotrophic denitrification (SADN) is a process based on S 0 , S 2− , S 2 O 3 2− Sulfur-containing reducing substances such as CO 2 , HCO 3 − , CO 3 2− As inorganic carbon sources, nitrate nitrogen (NO 3 − -N) Restore to N 2 SADN is a process of continuous acid production. As the reaction proceeds, the pH value of the reaction system will gradually decrease. In order to maintain an environment suitable for the growth of microorganisms, alkaline substances such as dolomite, limestone, egg shells, etc. need to be added to the system.

[0003] Compared with the traditional heterotrophic denitrification process, the SADN process does not require an external carbon source and has the advantages of low sludge production and low operating costs. 2− and S 2 O 3 2− In comparison, sulfur (S 0 ) is the most commonly used electron donor for SADN process because it is easy to obtain raw materials and has low cost. However, sulfur has very low water solubility (only 5 μg / L is dissolved at 25°C), which leads to its poor bioavailability and limits the denitrification rate of SADN (the denitrification load is usually less than 0.24 kg NO 3 − -N / m 3 ·d), which affects the widespread application of this process. Although SADN can achieve more efficient denitrification efficiency by coupling with other technologies (such as heterotrophic denitrification, anaerobic ammonium oxidation, and electrochemical hydrogen production), there are disadvantages such as substrate competition and nitrite accumulation during the experiment, and it has not yet been applied in large-scale engineering.

[0004] Currently, a lot of research is devoted to exploring how to improve the efficiency of electrons from S 0 transfer to sulfur-oxidizing denitrifying bacteria for NO 3 −-N reduction transfer rate, thereby increasing the SADN rate. Studies have shown that under moderately alkaline conditions, elemental sulfur and sulfide spontaneously react to form polysulfide (S n 2- ). 0 In comparison, S n 2- The bioavailability of S n 2- After being generated, it can be rapidly utilized by sulfur-oxidizing denitrifying bacteria to rapidly reduce NO 3 − -N.

[0005] However, S n 2− It is expensive and unstable, difficult to store for a long time, and not suitable for direct addition to sewage treatment plants. Although adding sodium sulfide / sodium hydrosulfide reagents can promote the generation of S n 2− However, sulfide has safety risks in transportation, use and storage. Studies have shown that adding external carbon sources can promote the activity of heterotrophic sulfur-reducing bacteria, thereby reducing elemental sulfur / sulfate to sulfide and promoting S n 2− However, the amount of organic carbon source added is difficult to control accurately. At the same time, the addition of carbon source introduces heterotrophic denitrification. Compared with heterotrophic bacteria, autotrophic bacteria have a longer generation time and a slower growth rate, and are prone to substrate (such as NO 3 − -N) competition, resulting in poor operational stability. To overcome the above shortcomings, some studies have been conducted on S 0 The pilot reactor of the mediated SADN was inoculated with sulfur dismutating bacteria and sulfur oxidizing denitrifying bacteria, and sufficient alkalinity (1 g / L NaHCO 3 ) to control the pH of the water body, maintain the symbiotic and cooperative relationship between the bacteria, so that sulfide is generated in the system and then further generates S n 2− , S n 2− , S 0 Together with sulfide, it acts as an electron donor, greatly improving the denitrification rate under the action of sulfur-oxidizing denitrifying bacteria. However, the material used in this implementation is sulfur, which is highly dangerous and not suitable for large-scale engineering applications. Other studies have added elemental sulfur conversion agents containing disulfide bonds / thiol groups, and compounded sulfur and adhesives to form composite fillers. Laboratory pilot tests have proved that elemental sulfur conversion agents promote S 0 Convert to S n 2− , thereby improving the denitrification efficiency. However, the elemental sulfur conversion agent required for this technology is expensive, which greatly increases the operating cost and is not suitable for large-scale production.

[0006] It can be seen that there is still room for improvement and enhancement in the existing technology. Summary of the invention

[0007] The present invention is directed to solving the above-referenced problems and other problems.

[0008] Another object of the present invention may be to increase the denitrification rate of sulfur-based composite fillers.

[0009] Yet another object of the present invention may be to increase the porosity of the sulfur-based composite filler.

[0010] Another object of the present invention may be to provide a sulfur-based composite filler with high strength.

[0011] The objects of the present invention are not limited to the above-mentioned objects, and those skilled in the art will be able to clearly understand other objects not mentioned through the following description.

[0012] In order to achieve the above objectives, this application adopts the following technical solutions: On the one hand, the present application discloses a method for preparing a sulfur-based composite filler, wherein the sulfur-based composite filler comprises sulfur, an alkaline material, an adhesive and a pore-forming agent, and the preparation method comprises the following steps: step one, grinding the sulfur, the alkaline material, the adhesive and the pore-forming agent into powder and mixing them evenly; step two, using a granulator to make the ground raw materials into particles; step three, heating and drying the particles; step four, heating the dried particles at 112-165° C. for 10-180 min until the sulfur on the surface of the particles melts, and then cooling to room temperature to fix the particles.

[0013] In some embodiments of the present application, the step 1 specifically includes: grinding sulfur, alkaline material, binder and pore-forming agent into powder with a particle size of 60-200 mesh.

[0014] In some embodiments of the present application, the particle size of the particles prepared in step 2 is 3-5 mm.

[0015] In some embodiments of the present application, the step three specifically includes: placing the particles prepared in step two in an oven and drying at 40-80° C. for 1.0-3.5 h.

[0016] In some embodiments of the present application, step four specifically includes: placing the dried particles in an oven or a muffle furnace, and heating them at 140~165°C for 10~20 min; or, placing the dried particles in an oven or a muffle furnace, and heating them at 112°C for 2.5~3 h.

[0017] In some embodiments of the present application, in the sulfur-based composite filler, the weight ratio of sulfur, alkaline material, binder and pore-forming agent is (20-30): (2-6): (1-3): (1-3).

[0018] In some embodiments of the present application, the alkaline material includes one or a combination of more of concrete, cement, gypsum, quicklime, limestone, sodium bicarbonate and sodium carbonate.

[0019] In some embodiments of the present application, the adhesive includes one or a combination of multiple of cement, gypsum, quicklime, limestone and clay.

[0020] In some embodiments of the present application, the preparation method further comprises: step five, loading sulfur disproportionating bacteria on the surface of the shaped particles.

[0021] In some embodiments of the present application, the step five specifically includes: spraying a sulfur disproportionate bacteria liquid on the surface of the shaped filler particles so that the sulfur disproportionate bacteria are loaded onto the filler particles; or, mixing and culturing the shaped filler particles with the sulfur disproportionate bacteria liquid so that the sulfur disproportionate bacteria are loaded onto the filler particles.

[0022] Another aspect of the present application also provides a sulfur-based composite filler, wherein the filler is Prepared by a preparation method as described above.

[0023] Beneficial effects: According to at least one of the embodiments of the present application, the uniformity of the filler is improved by grinding, mixing and granulating sulfur, alkaline material, binder and pore former.

[0024] According to at least one of the embodiments of the present application, by drying the granulated filler particles and then shaping them, it is possible to prevent the filler particles from sticking together, thereby ensuring the uniformity of the filler particles and a larger specific surface area.

[0025] According to at least one of the embodiments of the present application, the filler particles are heated at 112-150°C for 10-180 minutes to melt the sulfur on the surface of the particles, thereby increasing the hardness of the filler particles, reducing the dissolution rate of the filler in water, and providing a larger porosity inside the particles, thereby being able to load more bacterial agents. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of the denitrification rate of the sulfur-based composite filler provided in this application at different hydraulic retention times in laboratory simulated sewage.

[0027] Figure 2 Schematic diagram of the denitrification rate of the sulfur-based composite filler provided in this application at different hydraulic retention times in real rural domestic sewage. DETAILED DESCRIPTION

[0028] The present application provides a sulfur-based composite filler and a preparation method thereof. To make the purpose, technical solution and effect of the present application clearer and more specific, the present application is further described in detail with reference to the accompanying drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and are not used to limit the present application.

[0029] In the biochemical treatment of sewage, the filler provides a place for microorganisms to live. Therefore, the performance of the filler affects the growth, reproduction and shedding of microorganisms, which in turn directly affects the effect of sewage treatment.

[0030] The present application provides a method for preparing a sulfur-based composite filler. The sulfur-based composite filler comprises raw materials including sulfur, an alkaline material, an adhesive and a pore-forming agent.

[0031] Sulfur can react with other components to form a hardened network structure, giving the filler a certain strength and stability.

[0032] The alkaline material provides alkalinity to the filler, neutralizes the acidity produced during the growth of microorganisms, and provides a suitable growth environment for microorganisms.

[0033] The binder is used to bind the sulfur, alkaline material and pore former together so that they can form uniform and structurally stable particles.

[0034] The pore-forming agent can create gaps on the filler particles, allowing microorganisms to grow, reproduce and attach in the gaps between the particles. By adjusting the addition ratio of the pore-forming agent, the pore structure and density of the filler can be adjusted, thereby optimizing the physical properties of the filler and the sewage treatment effect.

[0035] Specifically, the preparation method comprises the following steps: Step 1: Grind sulfur, alkaline material, adhesive and pore-forming agent into powder and mix them evenly. Grinding the raw materials into powder can improve the uniformity of the filler and enable the raw materials to be better combined, which is convenient for subsequent granulation.

[0036] In some embodiments of the present application, sulfur, alkaline materials, adhesives and pore-forming agents can be ground to a particle size of 60 to 200 mesh, such as 60 mesh, 80 mesh, 90 mesh, 100 mesh, 110 mesh, 120 mesh, 150 mesh, 180 mesh, 200 mesh, etc., which not only ensures that the above raw materials have sufficient fineness and improves the uniformity of the filler, but also enables the various materials to be well combined. In addition, particles of this size are easy to grind and are not difficult to achieve without requiring excessively high process difficulty.

[0037] Step 2: Use a granulator to make the ground raw materials into granules to make the particle size of the filler more uniform. Compared with block fillers, granules can increase the overall specific surface area of ​​the filler, allowing more bacterial agents to attach and improve the denitrification effect.

[0038] The particle size of the ground raw materials after granulation can be 3~5 mm with high uniformity. If the particle size is too small, the particles are easy to stick together, reducing the specific surface area of ​​the filler. If the particle size is too large, the uniformity of the filler is low when used, thus affecting the denitrification effect.

[0039] Step three, placing the granulated filler particles in an oven, heating and drying them to reduce the moisture in the particles so that the filler particles can be better shaped in subsequent processes.

[0040] Filler particles can be dried by heating at 40-80°C for 1.0-3.5 h. Within this temperature and time range, the moisture in the filler particles can be basically removed without affecting the binding force of the components in the particles. If the heating temperature is too high, the surface of the filler particles may be charred, affecting the quality of the filler. If the heating temperature is too low, the evaporation of moisture is slow, reducing the preparation efficiency. If the heating time is too short, the moisture may not evaporate completely.

[0041] Illustratively, the filler particles may be heated at 40° C. for 3.5 h.

[0042] As another example, the filler particles may be heated at 55°C for 3.0 h.

[0043] Alternatively, the filler particles can be heated at 70°C for 2.0 h.

[0044] Alternatively, the filler particles can be heated at 80°C for 1.0 h.

[0045] Step 4: Heat the dried filler particles at 112-165°C for 10-180 minutes until the sulfur on the surface of the filler particles melts, and then cool to room temperature to set. The filler particles are heated until the sulfur on the surface just melts, and after cooling to room temperature to set, the sulfur solidifies and forms a protective layer with high hardness on the surface of the filler particles by forming a cross-linked structure, which greatly improves the hardness of the particles, thereby reducing the dissolution rate of the particles in water.

[0046] The filler particles are heated within the above temperature range to heat the sulfur into a molten state. During the heating process, the temperature of the particle surface is higher, and the sulfur on the particle surface begins to melt first. At this time, the sulfur inside the particle has not melted yet and is still in a porous structure. Controlling the heating temperature and the length of the heating time can control the melting degree of the sulfur in the filler particles.

[0047] In some embodiments of the present application, the dried filler particles can be placed in an oven or a muffle furnace and heated at 140-150°C for 10-20 min. Under this process, the shape of the particles will not change, the sulfur on the surface of the particles will just melt, while the sulfur inside the particles will not melt. The interior of the particles is still porous, has a large specific surface area, has a large adsorption capacity, and can adsorb more bacterial agents.

[0048] It is worth noting that the higher the heating temperature, the shorter the corresponding heating time, and the lower the heating temperature, the longer the heating time.

[0049] If the filler particles are heated at 120°C for 3 h, the particles have basically melted, the shape of the particles has changed, and there is basically no porous structure inside the filler, which reduces the adsorption capacity of the filler particles.

[0050] In some embodiments of the present application, in the sulfur-based composite filler, the weight ratio of sulfur, alkaline material, binder and pore-forming agent is (20-30): (2-6): (1-3): (1-3).

[0051] The sulfur content in the filler is not less than 70%, ensuring that the filler can load the amount of sulfur disproportionate bacteria. The alkaline material can just neutralize the acid produced during the growth of microorganisms, providing the most suitable growth environment for microorganisms.

[0052] The viscosity of the raw materials affects the granulation size of the filler particles. The higher the viscosity of the raw materials, the larger the finished particles; the lower the viscosity of the raw materials, the smaller the finished particles. The addition ratio of the above-mentioned binder makes the viscosity of the raw materials appropriate, and after granulation, the particle size of 3~5 mm is obtained, and the uniformity is high.

[0053] The pore-forming agent in the above proportion not only makes the filler particles have a larger porosity, increases the specific surface area of ​​the filler, is conducive to the attachment and growth of microorganisms, and improves the sewage treatment efficiency, but also does not affect the integrity of the filler. The filler can also present a granular shape with stable shape.

[0054] The pore-forming agent can be sodium carbonate or sodium bicarbonate. Sodium carbonate or sodium bicarbonate has good dispersibility and can be evenly dispersed in the filler so that the filler particles can evenly generate gaps, improve the structural stability of the filler and facilitate the attachment and growth of microorganisms. Sodium carbonate or sodium bicarbonate is non-toxic and harmless, has little impact on the environment, and conforms to the principle of green chemistry. In addition, the price of sodium carbonate or sodium bicarbonate is relatively low, which can reduce the product cost of the filler.

[0055] The alkaline material may include one or a combination of more than one of concrete, cement, gypsum, quicklime, limestone, sodium bicarbonate and sodium carbonate.

[0056] The binder may include one or a combination of cement, gypsum, quicklime, limestone and clay.

[0057] Advantageously, cement has strong bonding ability and durability, undergoes hydration reaction in water, and gradually increases in strength over time. In addition, cement can withstand greater pressure and tension after solidification. Using cement as a binder in fillers, the structure of the resulting filler particles is very stable.

[0058] Gypsum is a relatively mild bonding material that hardens quickly and is easy to shape and process. Fillers using gypsum as a binder tend to form particles of uniform size during the granulation process. However, the bonding ability, water resistance and durability of gypsum are not as good as those of cement.

[0059] In some embodiments of the present application, the method for preparing the filler further comprises: Step 5: loading sulfur disproportionate bacteria on the surface of the shaped particles.

[0060] Specifically, step five may include spraying sulfur disproportionate bacteria liquid on the surface of the shaped filler particles so that the sulfur disproportionate bacteria are loaded onto the filler particles; or, mixing and culturing the shaped filler particles with the sulfur disproportionate bacteria liquid so that the sulfur disproportionate bacteria are loaded onto the filler particles.

[0061] In order to better explain the scheme of the present application, some specific embodiments are provided below to further illustrate the present application.

[0062] Unless otherwise specified, the raw materials, reagents, test equipment, etc. used in the following embodiments are common commercially available products.

[0063] Example 1 Take sulfur, limestone, cement and sodium bicarbonate in a mass ratio of 22:6:2:1 respectively.

[0064] The above raw materials are ground to about 80 meshes with a grinder and mixed evenly. The mixed raw materials are placed in a granulator for granulation. The filler particles obtained by granulation are placed in an oven and heated at 68°C for 2.5 hours, then heated to 140°C for 20 minutes until the sulfur on the surface of the particles melts, and then cooled to room temperature to shape the particles. A protective layer with high hardness is formed on the surface of the cooled particles.

[0065] Example 2 Take sulfur, concrete, gypsum and sodium bicarbonate in a mass ratio of 27:4:3:2 respectively.

[0066] The above raw materials are ground to about 100 mesh with a grinder and mixed evenly. The mixed raw materials are placed in a granulator for granulation. The filler particles obtained by granulation are then placed in an oven and heated at 70°C for 2 hours, then heated to 165°C for 10 minutes until the sulfur on the surface of the particles melts, and then cooled to room temperature to shape the particles. A protective layer with high hardness is formed on the surface of the cooled particles.

[0067] The Mohs hardness, porosity, specific surface area, sulfur dissolution rate, basicity, apparent density and bulk density of the fillers prepared in the above Example 1 and Example 2 were tested respectively. The test results are shown in Table 1.

[0068] Table 1: Mohs hardness, porosity, specific surface area, sulfur dissolution rate, basicity, apparent density and bulk density of the fillers prepared in Example 1 and Example 2 Note: The larger the Mohs hardness number, the stronger the hardness.

[0069] As can be seen from Table 1, the fillers prepared in Example 1 and Example 2 have high porosity and a large specific surface area, and can carry more microorganisms, thereby improving the electron mass transfer efficiency; the particles have high hardness and alkalinity, and have strong pH buffering capacity during actual use, which greatly reduces the amount of additional alkalinity added, thereby reducing the process cost.

[0070] Example 3 Activated sludge was introduced, sulfur disproportionation bacteria were inoculated into the activated sludge, and nutrient solution was added to provide conditions suitable for the growth of sulfur disproportionation bacteria to enrich sulfur disproportionation bacteria. When the bacterial solution can stably produce 10-20 mg S / L sulfide, the bacterial solution is successfully domesticated.

[0071] The filler prepared in Example 2 was placed in the enriched sulfur disproportionated bacteria solution, and a nutrient solution was added to successfully load the sulfur disproportionated bacteria into the filler, thereby obtaining a filler loaded with the bacteria solution.

[0072] It is understandable that the above-mentioned nutrient solution can adopt the nutrient components suitable for the growth of strains including trace elements, alkali solution and the like in the prior art, which is not limited here.

[0073] Example 4 The filler prepared in Example 3 was applied to a laboratory reactor. The simulated sewage quality was nitrogen-containing sewage. The influent nitrate nitrogen concentration was maintained at 40 mg / L. The filling ratio of the filler was 66%. The hydraulic retention time was 23 min. In the reactor integrating sulfur disproportionation and sulfur autotrophic denitrification, the nitrate nitrogen removal rate was 62-72%, and the average denitrification rate was 1.59 kg NO 3 − -N / (m 3·d). In addition, an additional sulfur disproportionation reactor was set up, and the sulfide and polysulfide produced by the reactor were introduced into the existing sulfur disproportionation and sulfur autotrophic denitrification integrated reactor in series, so that the generated sulfide and polysulfide were enhanced for denitrification. The results showed that the nitrate nitrogen removal rate was as high as more than 90%, and the denitrification rate was as high as 1.77~2.35 kg NO 3 − -N / (m 3 ·d).

[0074] Example 5 The effluent of actual rural domestic sewage was introduced, and the filler loaded with bacterial liquid in Example 2 was placed in the above sewage for a small-scale denitrification test to verify the denitrification effect of the filler. The influent nitrate nitrogen concentration was basically 40-55 mg / L, the filling ratio of the filler was 53%, and the hydraulic retention time was 2 h, 1.5 h, 1 h and 0.5 h (all in the dry season). The test results showed that as the hydraulic retention time gradually shortened from 2 h to 0.5 h, the average denitrification rate increased from 0.56 kg NO 3 − -N / (m 3 d) Gradually increase to 1.14 kg NO 3 − -N / (m 3 ·d). The removal rate of nitrate nitrogen is basically stable at 50%~80%, and the highest is 100%. In addition, the filler samples have high uniformity and beautiful appearance, which meets the needs of commercial production and large-scale application in actual sewage denitrification scenarios.

[0075] It is understandable that those skilled in the art can make equivalent substitutions or changes based on the technical solution and inventive concept of the present application, and all these changes or substitutions should fall within the protection scope of the claims attached to the present application.

Claims

1. A method for preparing a sulfur-based composite filler, characterized in that: The sulfur-based composite filler includes sulfur Sulfur, alkaline material, adhesive and pore-forming agent, the preparation method comprises the following steps: step 1, grinding sulfur, alkaline material, adhesive and pore-forming agent into powder and mixing them evenly; step 2, using a granulator to make the ground raw materials into particles; step 3, heating and drying the particles; step 4, heating the dried particles at 112-165°C for 10-180min until the sulfur on the surface of the particles melts, and then cooling to room temperature to fix the particles.

2. The preparation method according to claim 1, characterized in that: The step 1 specifically comprises: grinding sulfur, alkaline material, binder and pore-forming agent into powder with a particle size of 60-200 mesh.

3. The preparation method according to claim 1, characterized in that: The particles prepared in step 2 The particle size is 3~5 mm.

4. The preparation method according to claim 1, characterized in that: The step three specifically includes: Place the particles prepared in step 2 in an oven and dry at 40-80°C for 1.0-3.5 h.

5. The preparation method according to claim 1, characterized in that: The step 4 specifically includes: The dried particles are placed in an oven or a muffle furnace and heated at 140-165°C for 10-20 min; alternatively, the dried particles are placed in an oven or a muffle furnace and heated at 112°C for 2.5-3 h.

6. The preparation method according to any one of claims 1 to 5, characterized in that The sulfur-based composite In the filler, the weight ratio of sulfur, alkaline material, binder and pore-forming agent is (20-30): (2-6): (1-3): (1-3).

7. The preparation method according to claim 6, characterized in that: The alkaline material includes coagulation One or a combination of soil, cement, gypsum, quicklime, limestone, sodium bicarbonate and sodium carbonate.

8. The preparation method according to claim 6, characterized in that: The adhesive includes cement, One or a combination of gypsum, quicklime, limestone and clay.

9. The preparation method according to any one of claims 1 to 5, characterized in that The preparation method The method also includes: step five, loading sulfur disproportionating bacteria on the surface of the shaped particles.

10. The preparation method according to claim 9, characterized in that: The step five specifically includes: The sulphur disproportionate bacteria liquid is sprayed on the surface of the shaped filler particles so that the sulphur disproportionate bacteria are loaded on the filler particles; or the shaped filler particles are mixed and cultured with the sulphur disproportionate bacteria liquid so that the sulphur disproportionate bacteria are loaded on the filler particles.

11. A sulfur-based composite filler, characterized in that: The filler is prepared by the preparation method according to any one of claims 1 to 10.

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