Sulfur-based composite filler and method for producing the same

Abstract

The application discloses a sulfur-based composite filler and a preparation method thereof. The sulfur-based composite filler comprises sulfur, an alkaline material, a binder and a pore-forming agent. The preparation method comprises the following steps: grinding the sulfur, the alkaline material, the binder and the pore-forming agent into powders and uniformly mixing the powders, using a granulator to make the ground raw materials into granules, heating and drying the granules, heating the dried granules at 112-165 DEG C for 10-180 min until the sulfur on the surface of the granules is melted, and then cooling the granules to room temperature to be shaped, so that the filler forms granules with high hardness, the dissolution rate of the filler in water is reduced, the internal part of the granules has high porosity, more bacterial agents can be loaded, nitrate in wastewater can be removed efficiently and quickly, the filler prepared by the method has strong alkalinity, and when the filler is applied to sewage treatment, the addition of alkalinity can be reduced, and the operation cost is reduced.

Description

TECHNICAL FIELD

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

[0002] Sulfur autotrophic denitrification (SADN) process is a process of reducing nitrate nitrogen (NO3 − -N) to N2 by using S 0 , S 2− , S2O3 2− and other sulfur-containing reducing substances as electron donors, and CO2, HCO3 − , CO3 2− as inorganic carbon source. SADN is a process of continuously producing acid, and the pH value of the reaction system will gradually decrease as the reaction proceeds. In order to maintain a suitable environment for microbial growth, alkaline substances such as dolomite, limestone, eggshells, etc. need to be added to the system.

[0003] Compared with traditional heterotrophic denitrification denitrification process, SADN process does not need external carbon source, and has the advantages of low sludge yield and low operation cost. Compared with S 2− and S2O3 2− , sulfur (S 0 ) is easy to obtain and has low cost, and is the most common electron donor for realizing SADN process application. However, sulfur has very low water solubility (only 5 μg / L at 25℃), which leads to poor bioavailability and limits the denitrification rate of SADN (denitrification load is usually lower than 0.24 kg NO3 − -N / m 3 ·d), affecting the wide application of the process. Although SADN coupled with other technologies (such as heterotrophic denitrification, anaerobic ammonia oxidation, and electrochemical hydrogen production) can achieve higher denitrification efficiency, there are disadvantages such as substrate competition and nitrite accumulation in the test process, and large-scale engineering application has not been realized.

[0004] Currently, a large number of studies are devoted to exploring how to improve the transfer rate of electrons from S 0 to sulfur-oxidizing denitrifying bacteria for NO3 − -N reduction, so as to improve the SADN rate. Studies have shown that under the condition of moderate alkalinity, elemental sulfur and sulfide spontaneously react to form polysulfide (S n 2- Compared with S 0 , S n 2- has nearly 40 times higher bioavailability, and S n 2-After being generated, it can be quickly utilized by sulfur-oxidizing denitrifying bacteria and rapidly reduced to NO3 − -N.

[0005] However, S n 2− is expensive and unstable, and is difficult to store for a long time, so it is not suitable for direct addition to a sewage treatment plant. Although the addition of sodium sulfide / sodium hydrosulfide reagent can promote the generation of S n 2− , there are safety risks in the transportation, use and storage of sulfides. Studies have shown that the addition of a carbon source can promote the activity of heterotrophic sulfur-reducing bacteria, thereby reducing elemental sulfur / sulfate to sulfide and promoting the generation of S n 2− . However, the amount of organic carbon source added is difficult to accurately control, and the addition of a carbon source introduces heterotrophic denitrification. Autotrophic bacteria have a long generation time and a slow growth rate compared to heterotrophic bacteria, and are easily disadvantaged in substrate (such as NO3 − -N) competition, resulting in poor operational stability. To overcome the above shortcomings, some studies inoculate sulfur-disulfide bacteria and sulfur-oxidizing denitrifying bacteria into a S 0 mediated SADN small-scale reactor, and additionally provide sufficient alkalinity (1 g / L NaHCO3) to control the pH of the water body and maintain the symbiosis and cooperation between the strains, so that the sulfide generated in the system is further converted to S n 2− , S n 2− , S 0 and sulfide together as an electron donor greatly improve 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. Another study adds an elemental sulfur conversion agent containing a disulfide bond / thiol, and combines sulfur and a binder to form a composite filler. Laboratory small-scale tests have shown that the elemental sulfur conversion agent promotes the conversion of S 0 to S n 2− , thereby improving the denitrification efficiency. However, the elemental sulfur conversion agent required by this technology is expensive, greatly increasing the operating cost, and is not suitable for large-scale production and use.

[0006] It can be seen that the existing technology still needs to be improved and improved. SUMMARY

[0007] The purpose of the present application is to solve the above problems and other problems.

[0008] Another purpose of the present application can be to improve the denitrification rate of the sulfur-based composite filler.

[0009] Still another purpose of the present application can be to improve the porosity of the sulfur-based composite filler.

[0010] Yet another object of the present application can be to provide a sulfur-based composite filler with high strength.

[0011] The objects of the present application are not limited to the above-mentioned objects, and other objects not mentioned above can be clearly understood by those skilled in the art through the following description.

[0012] In order to achieve the above-mentioned objects, the present application adopts the following technical solutions:

[0013] In one aspect, the present application discloses a preparation method of a sulfur-based composite filler, the sulfur-based composite filler comprising sulfur, alkaline material, binder and pore-forming agent, the preparation method comprising the following steps: step one, grinding the sulfur, alkaline material, binder and pore-forming agent into powder and mixing uniformly; step two, using a granulator to make the ground raw materials into granules; step three, heating and drying the above-mentioned granules; step four, heating the dried granules at 112-165℃ for 10-180min until the sulfur on the surface of the granules melts, and then cooling to room temperature for setting.

[0014] In some embodiments of the present application, the step one specifically comprises grinding the sulfur, alkaline material, binder and pore-forming agent into powder with a particle size of 60-200 mesh.

[0015] In some embodiments of the present application, the particle size of the granules prepared in the step two is 3-5mm.

[0016] In some embodiments of the present application, the step three specifically comprises placing the granules prepared in the step two in an oven and drying at 40-80℃ for 1.0-3.5h.

[0017] In some embodiments of the present application, the step four specifically comprises placing the dried granules in an oven or muffle furnace and heating at 140-165℃ for 10-20min; or placing the dried granules in an oven or muffle furnace and heating at 112℃ for 2.5-3h.

[0018] 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).

[0019] In some embodiments of the present application, the alkaline material comprises one or a combination of multiple kinds of concrete, cement, gypsum, quicklime, limestone, sodium bicarbonate and sodium carbonate.

[0020] In some embodiments of the present application, the binder comprises one or a combination of multiple kinds of cement, gypsum, quicklime, limestone and clay.

[0021] In some embodiments of the present application, the preparation method further comprises: step five, loading sulfur-dispersing bacteria on the surface of the shaped particles.

[0022] In some embodiments of the present application, step five specifically comprises: spraying a sulfur-dispersing bacteria solution on the surface of the shaped filler particles, so that the sulfur-dispersing bacteria are loaded on the filler particles; or, mixing and culturing the shaped filler particles with the sulfur-dispersing bacteria solution, so that the sulfur-dispersing bacteria are loaded on the filler particles.

[0023] Another aspect of the present application also provides a sulfur-based composite filler prepared by the method as described above.

[0024] The sulfur-based composite filler is prepared by the method as described in one aspect.

[0025] Beneficial effects:

[0026] According to at least one of the embodiments of the present application, by grinding, mixing and uniformly granulating sulfur, alkaline material, binder and pore-forming agent, the uniformity of the filler is improved.

[0027] According to at least one of the embodiments of the present application, by drying the granulated filler particles and then shaping, the filler particles can be prevented from sticking together, ensuring the uniformity of the filler particles and having a larger specific surface area.

[0028] According to at least one of the embodiments of the present application, by heating the filler particles at 112-150℃ for 10-180min, the sulfur on the surface of the particles is melted, the hardness of the filler particles is improved, the dissolution rate of the filler in water is reduced, and the particles have a larger porosity, which can load more bacteria agents. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 A schematic diagram of the nitrogen removal rate of the sulfur-based composite filler provided by the present application under different hydraulic retention times in laboratory simulated sewage.

[0030] Figure 2 A schematic diagram of the nitrogen removal rate of the sulfur-based composite filler provided by the present application under different hydraulic retention times in real rural domestic sewage. DETAILED DESCRIPTION

[0031] The present application provides a sulfur-based composite filler and a preparation method thereof. In order to make the purpose, technical scheme and effects of the present application more clear and explicit, the present application is further described in detail below with reference to the drawings and examples. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application.

[0032] In sewage biochemical treatment, filler provides a habitat for microorganisms, therefore, the performance of the filler affects the growth, reproduction and shedding of microorganisms, and further directly affects the effect of sewage treatment.

[0033] The application provides a preparation method of a sulfur-based composite filler. The raw materials of the sulfur-based composite filler include sulfur, alkaline material, binder and pore-forming agent.

[0034] The sulfur can react with other components to form a hardened network structure, thereby giving the filler certain strength and stability.

[0035] The alkaline material provides alkalinity for the filler, neutralizes the acidity generated in the microbial growth process, and provides a suitable growth environment for the microorganisms.

[0036] The binder is used to bind the sulfur, alkaline material and pore-forming agent together, so that they can form uniform and structurally stable granules.

[0037] The pore-forming agent can generate voids on the filler particles, so that the microorganisms can grow, reproduce and adhere in the voids of the particles. By adjusting the addition proportion of the pore-forming agent, the pore structure and density of the filler can be adjusted, thereby optimizing the physical properties and sewage treatment effect of the filler.

[0038] Specifically, the preparation method comprises the following steps:

[0039] In step one, the sulfur, alkaline material, binder and pore-forming agent are ground into powders and uniformly mixed. Grinding the raw materials into powders can improve the uniformity of the filler and enable the raw materials to be better combined, thereby facilitating subsequent granulation.

[0040] In some embodiments of the application, the sulfur, alkaline material, binder and pore-forming agent can be ground to a particle size of 60-200 mesh, such as 60 mesh, 80 mesh, 90 mesh, 100 mesh, 110 mesh, 120 mesh, 150 mesh, 180 mesh, 200 mesh, etc. This ensures that the above-mentioned raw materials have sufficient fineness, improves the uniformity of the filler, enables the materials to be well combined, and the particles of this size are easy to grind and operate, do not require high process difficulty.

[0041] In step two, a granulator is used to make the ground raw materials into granules, so that the particle size of the filler is more uniform. Compared with blocky fillers, granular fillers can increase the specific surface area of the whole filler, so that more bacterial agents can be attached, thereby improving the denitrification effect.

[0042] 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, thereby affecting the denitrification effect.

[0043] Step three, the granulated filler particles are placed in an oven to be heated and dried to reduce the moisture in the particles so that the filler particles can be better shaped in the subsequent process.

[0044] The filler particles can be heated and dried at 40-80℃ for 1.0-3.5h. Within this temperature and time range, the moisture in the filler particles can be substantially 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 carbonized, 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 be completely evaporated.

[0045] For example, the filler particles can be heated at 40℃ for 3.5h.

[0046] For another example, the filler particles can be heated at 55℃ for 3.0h.

[0047] Alternatively, the filler particles can be heated at 70℃ for 2.0h.

[0048] Alternatively, the filler particles can be heated at 80℃ for 1.0h.

[0049] Step four, the above dried filler particles are heated at 112-165℃ for 10-180min until the sulfur on the surface of the filler particles is just melted, and then cooled to room temperature to be shaped. After the filler particles are heated to the point where the sulfur on the surface is just melted and cooled to room temperature to be shaped, the sulfur solidifies and forms a hard protective layer on the surface of the filler particles by forming a cross-linked structure, greatly improving the hardness of the particles, thereby reducing the dissolution rate of the particles in water.

[0050] Heating the filler particles within the above temperature range can heat the sulfur to a molten state. During the heating process, the temperature on the surface of the particles is high, and the sulfur on the surface of the particles starts to melt first. At this time, the sulfur inside the particles has not yet melted 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.

[0051] In some embodiments of the present application, the dried filler particles can be placed in an oven or muffle furnace and heated at 140-150℃ for 10-20min. Under this process, the shape of the particles does not change, the sulfur on the surface of the particles just melts, and the sulfur inside the particles has not yet melted, and the particles inside are still in a porous structure, have a large specific surface area, and have a large adsorption capacity, which can adsorb more fungicides.

[0052] 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.

[0053] If the filler particles are heated at 120℃ for 3 hours, the particles have been essentially melted, the shape of the particles has changed, and the internal structure of the filler is essentially free of porosity, reducing the adsorption capacity of the filler particles.

[0054] In some embodiments of the present application, the weight ratio of sulfur, alkaline material, binder and pore-forming agent in the sulfur-based composite filler is (20-30):(2-6):(1-3):(1-3).

[0055] In the filler, the content of sulfur is not less than 70%, which ensures the amount of sulfur-disulfur bacteria that can be loaded on the filler. The alkaline material can just neutralize the acid produced during microbial growth, providing the most suitable growth environment for the microorganisms.

[0056] The viscosity of the raw materials affects the size of the filler particles. The higher the viscosity of the raw materials, the larger the finished particles; the smaller the viscosity of the raw materials, the smaller the finished particles. The addition of the above-mentioned binder makes the viscosity of the raw materials suitable, and the particle size of the particles after granulation is 3-5 mm, with high uniformity.

[0057] The above-mentioned proportion of pore-forming agent not only makes the filler particles have a larger porosity, increases the specific surface area of the filler, and is beneficial to the adhesion and growth of microorganisms, but also does not affect the integrity of the filler, and the filler can also present a stable particle shape.

[0058] The pore-forming agent can be sodium carbonate or sodium bicarbonate. Sodium carbonate or sodium bicarbonate has good dispersibility and can be uniformly dispersed in the filler to make the filler particles uniformly produce voids, improve the structural stability of the filler, and be beneficial to the adhesion and growth of microorganisms. Sodium carbonate or sodium bicarbonate is non-toxic and harmless, has little impact on the environment, and meets the principles of green chemistry. In addition, sodium carbonate or sodium bicarbonate is relatively low in price, which can reduce the product cost of the filler.

[0059] The alkaline material can include one or a combination of more than one of concrete, cement, gypsum, quicklime, limestone, sodium bicarbonate and sodium carbonate.

[0060] The binder can include one or a combination of more than one of cement, gypsum, quicklime, limestone and clay.

[0061] More preferably, cement has strong bonding ability and durability, will undergo hydration reaction in water, and the strength will gradually increase over time. Moreover, cement can withstand a large pressure and tensile force after solidification. The use of cement as a binder in the filler results in a very stable structure of the filler particles.

[0062] Gypsum is a relatively mild adhesive material, which hardens fast, and is easy to shape and process. Fillers using gypsum as the adhesive material are easy to form uniform particles in the granulation process. However, the adhesive capacity, water resistance and durability of gypsum are insufficient compared to cement.

[0063] In some embodiments of the present application, the method for preparing the filler further comprises:

[0064] Step five, loading sulfur disulfide bacteria on the surface of the shaped particles.

[0065] Specifically, step five can include spraying a sulfur disulfide bacteria solution on the surface of the shaped filler particles, so that the sulfur disulfide bacteria are loaded onto the filler particles; or, mixing and culturing the shaped filler particles with the sulfur disulfide bacteria solution, so that the sulfur disulfide bacteria are loaded onto the filler particles.

[0066] To better explain the scheme of the present application, some specific embodiments are provided below to further illustrate the present application.

[0067] Unless otherwise specified, the raw materials, reagents, test equipment, etc. used in the following embodiments are all ordinary commercially available products.

[0068] Example 1

[0069] Sulfur, limestone, cement and sodium bicarbonate are taken in a mass ratio of 22:6:2:1, respectively.

[0070] The above raw materials are ground to about 80 mesh with a grinder and mixed uniformly. The mixed raw materials are placed in a granulator to granulate, and the filler particles obtained by granulation are placed in an oven at 68°C for heating for 2.5 h, and then the temperature is increased to 140°C for heating for 20 min, until the sulfur on the surface of the particles is melted, and then cooled to room temperature to shape the particles. A layer of high-hardness protective layer is formed on the surface of the cooled particles.

[0071] Example 2

[0072] Sulfur, concrete, gypsum and sodium bicarbonate are taken in a mass ratio of 27:4:3:2, respectively.

[0073] The above raw materials are ground to about 100 mesh with a grinder and mixed uniformly. The mixed raw materials are placed in a granulator to granulate, and the filler particles obtained by granulation are placed in an oven at 70°C for heating for 2 h, and then the temperature is increased to 165°C for heating for 10 min, until the sulfur on the surface of the particles is melted, and then cooled to room temperature to shape the particles. A layer of high-hardness protective layer is formed on the surface of the cooled particles.

[0074] The Mohs hardness, porosity, specific surface area, sulfur dissolution rate, alkalinity, apparent density and bulk density of the fillers prepared in the above Example 1 and Example 2 are tested, respectively, and the test results are shown in Table 1.

[0075] Table 1: Mohs hardness, porosity, specific surface area, sulfur dissolution rate, alkalinity, apparent density and bulk density of the fillers prepared in Example 1 and Example 2

[0076]

[0077] Note: The larger the Mohs hardness number level represents the stronger hardness.

[0078] As can be seen from Table 1, the fillers prepared in Example 1 and Example 2 have high porosity and large specific surface area, which can load more microorganisms and improve the electron mass transfer efficiency; the hardness and alkalinity of the particles are high, the pH buffering capacity is strong during actual use, which greatly reduces the additional alkalinity dosage, thereby reducing the process cost.

[0079] Example 3

[0080] The activated sludge is introduced, the sulfur disproportionating bacteria is inoculated into the activated sludge, and then the nutrient solution is added to provide suitable conditions for the growth of sulfur disproportionating bacteria to enrich the sulfur disproportionating bacteria. When the bacteria solution can stably produce 10-20 mg S / L sulfide, the bacteria solution is successfully domesticated.

[0081] The filler prepared in the above Example 2 is placed in the above enriched sulfur disproportionating bacteria solution, and the nutrient solution is added to successfully load the sulfur disproportionating bacteria into the filler, thereby obtaining the filler after loading the bacteria solution.

[0082] It can be understood that the above nutrient solution can use the nutrient components suitable for the growth of the strain including trace elements, alkali solution and the like in the prior art, which is not limited herein.

[0083] Example 4

[0084] The filler prepared in Example 3 is applied to a laboratory reactor, the simulated sewage water quality is nitrogen-containing sewage, the influent nitrate nitrogen concentration is maintained at 40 mg / L, the filling ratio of the filler is 66%, and the hydraulic retention time is 23 min. In the reactor integrating sulfur disproportionation and sulfur autotrophic denitrification, the nitrate nitrogen removal rate is 62-72%, and the average denitrification rate is 1.59 kg NO3 − -N / (m 3 ·d). In addition, a sulfur disproportionation reactor is additionally provided, and the sulfide and polysulfide generated by the reactor are introduced into the existing reactor integrating sulfur disproportionation and sulfur autotrophic denitrification in a series mode, so as to strengthen the denitrification of the generated sulfide and polysulfide. The results show that the nitrate nitrogen removal rate is as high as 90% or more, and the denitrification rate is as high as 1.77-2.35 kg NO3 − -N / (m 3 ·d).

[0085] Example 5

[0086] The effluent of the actual rural domestic sewage was introduced, and the filler after the bacteria solution in Example 2 was put into the above-mentioned sewage for small-scale denitrification test verification to test the denitrification effect of the filler. The concentration of nitrate nitrogen in the influent 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 dry season). The test results show that, with the hydraulic retention time gradually shortened from 2 h to 0.5 h, the average denitrification rate gradually increased from 0.56 kg NO3 − -N / (m 3 ·d) to 1.14 kg NO3 − -N / (m 3 ·d). The removal rate of nitrate nitrogen was basically stable at 50%-80%, and the highest reached 100%. In addition, the uniformity of the filler sample was high, and the appearance was beautiful, meeting the needs of commercial production and large-scale application in actual sewage denitrification scenarios.

[0087] It can be understood that, for those skilled in the art, equivalent replacements or changes can be made according to the technical solutions and inventive concepts of the present application, and all such changes or replacements shall belong to the protection scope of the claims attached hereto.

Claims

1. A method for preparing a sulfur-based composite filler, characterized in that, The sulfur-based composite filler includes sulfur, alkaline materials, binders, and pore-forming agents. The preparation method includes the following steps: Step 1, grinding sulfur, alkaline materials, binders, and pore-forming agents into powder and mixing them evenly; Step 2, using a granulator to make the ground raw materials into granules; Step 3, heating and drying the granules; Step 4, heating the dried granules at 140~165℃ for 10~20 min until the sulfur on the surface of the granules just melts, and then cooling to room temperature to set the shape. A protective shell is formed on the surface of the filler granules, and the interior of the granules is porous.

2. The preparation method according to claim 1, characterized in that, Step one specifically includes grinding sulfur, alkaline materials, adhesives and pore-forming agents into powder with a particle size of 60-200 mesh.

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

4. The preparation method according to claim 1, characterized in that, Step three specifically includes: placing the particles prepared in step two in an oven and drying them at 40~80℃ for 1.0~3.5 h.

5. The preparation method according to any one of claims 1 to 4, characterized in that, 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).

6. The preparation method according to claim 5, characterized in that, The alkaline material includes one or more of the following: concrete, cement, gypsum, quicklime, limestone, sodium bicarbonate, and sodium carbonate.

7. The preparation method according to claim 5, characterized in that, The adhesive comprises one or more of cement, gypsum, quicklime, limestone, and clay.

8. The preparation method according to any one of claims 1 to 4, characterized in that, The preparation method further includes: step five, loading sulfur dismutase bacteria onto the surface of the shaped particles.

9. The preparation method according to claim 8, characterized in that, Step five specifically includes: spraying sulfur dismutase solution onto the surface of the shaped filler particles so that sulfur dismutase bacteria are loaded onto the filler particles; or, mixing and culturing the shaped filler particles with sulfur dismutase solution so that sulfur dismutase bacteria are loaded onto the filler particles.

10. A sulfur-based composite filler, characterized in that, The filler is prepared by the preparation method according to any one of claims 1 to 9.

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