An autotrophic denitrification filler applicable to sewage with a low carbon-nitrogen ratio and a preparation method thereof

Abstract

The present invention discloses an autotrophic denitrification nitrogen removal filler suitable for low carbon-nitrogen ratio sewage and a preparation method thereof. The filler comprises the following raw materials by weight percentage: 40% - 45% of sulfoaluminate cement, 8.5% of silica fume, 1.5% of modified sodium percarbonate, 16.8% - 25.2% of sulfur powder, 16.8% - 25.2% of pyrite powder, and 3% - 8% of calcium carbonate powder. Experimental results show that the autotrophic denitrification filler provided by the present invention has excellent nitrogen removal effect on low carbon-nitrogen ratio sewage water body and can meet the technical requirements of deep denitrification treatment. In addition, for the autotrophic denitrification nitrogen removal filler provided by the present invention, its denitrification process is simple, without the need to use fuel to melt raw materials, and it can be applied to large-scale production and actual industrial applications. The microbial film hanging is fast, the denitrification efficiency is high, the raw materials are cheap and easy to obtain, the process is simple, and the requirements for equipment / environment are low. Therefore, it has broad development potential.

Description

Technical Field

[0001] The present invention relates to the field of denitrification treatment, and relates to an autotrophic denitrification filler suitable for low carbon-nitrogen ratio sewage and a preparation method thereof. Background Art

[0002] Industrial wastewater with high-concentration nitrate nitrogen has very low or even no organic matter content, but contains a relatively high concentration of nitrate nitrogen. Taking the steel industry as an example, it is an industrial industry with a large water consumption, and the wastewater discharged by it has the characteristics of low C / N. In addition, other wastewater with a relatively high organic nitrogen concentration cannot meet the discharge standard after ordinary biochemical treatment. It can only convert organic nitrogen into nitrate nitrogen, thus converting it into high-concentration nitrate nitrogen wastewater, such as chemical industrial wastewater, food wastewater, etc. In addition, the existing wastewater treatment process in sewage treatment plants has certain limitations. The secondary effluent still contains a certain concentration of total nitrogen, and it basically exists in the form of nitrate nitrogen. The COD in the secondary effluent is generally very low, with the characteristics of low C / N. The in-depth denitrification treatment of low C / N wastewater is imperative.

[0003] At present, the methods for removing nitrate nitrogen salts mainly include: physical technology, chemical treatment technology and biological treatment technology. Among them, physical technology includes: adsorption method, ion exchange method and membrane separation method, etc. The adsorption method is to use some materials with a large adsorption capacity and specific surface area to adsorb nitrate nitrogen, so as to achieve the removal of nitrate nitrogen. Its advantage is that the principle is simple and only a material with a large specific surface area needs to be made, but it is also limited by the high production cost of materials with a large adsorption capacity and specific surface area; the ion exchange method is to use the exchange ability of alkaline anion resin to exchange chloride or carbonate with nitrate nitrogen to remove nitrate nitrogen in water. This method is simple and efficient, easy to automate control, and recyclable, but there is a problem of treating the regeneration waste liquid, and it is not suitable for large-scale nitrate nitrogen salt pollution problems; the membrane separation method is to achieve the separation of the target component by applying an external driving force on both sides of the membrane. The membrane separation method mainly includes reverse osmosis method and electrodialysis method. Among them, the reverse osmosis method separates the solute and water through a reverse osmosis membrane, and then relies on an external pressure to make water molecules pass through the reverse osmosis membrane to achieve the purpose of separating and removing nitrate nitrogen. This separation technology can concentrate nitrate nitrogen and does not change its molecular form, which is convenient for subsequent collection and centralized treatment. Although the reverse osmosis method can concentrate nitrate nitrogen in water, the concentrated solution needs to be treated twice, which increases the treatment cost and energy consumption. At the same time, the reverse osmosis process will also remove the ions beneficial to the human body in the water; the electrodialysis membrane method uses a selective ion exchange membrane as the medium. Under the action of a direct current electric field, the nitrate nitrogen salt is separated from the water through the membrane and enters the high-concentration brine side, and the ion concentration difference between the fresh and concentrated chambers is increased to achieve the separation purpose. The removal efficiency of the electrodialysis membrane method is high, but the concentrated solution needs to be further treated, resulting in certain limitations in the application of this method.

[0004] Chemical treatment technology: Using active metals or catalysts to reduce nitrate nitrogen salts, the chemical reduction method has high efficiency, but is prone to producing by-products, causing secondary pollution. Although the above physical and chemical technologies have fast reactions, they have problems such as high cost, high energy consumption, and the generation of concentrated liquid and secondary pollution, and are not suitable for large-scale applications.

[0005] Biological treatment technology: Using the denitrification of microorganisms to remove nitrate nitrogen pollution, it can be divided into heterotrophic denitrification and autotrophic denitrification according to different required electron donors. The heterotrophic denitrification technology uses organic carbon sources as electron donors, such as glucose or sodium acetate, etc. The reaction rate is fast, but problems such as unstable dosing amount and secondary pollution of the effluent are likely to occur. The most commonly used autotrophic denitrification technology is sulfur autotrophic denitrification technology, which uses elemental sulfur or sulfur-containing compounds as electron donors, and reduces nitrate nitrogen to nitrogen gas through sulfur autotrophic denitrifying bacteria for removal. Although the sulfur autotrophic denitrification technology does not require an external carbon source and is suitable for nitrogen removal from low C / N wastewater, it will cause acidification of the effluent and an increase in sulfate concentration; furthermore, when using elemental sulfur for sulfur autotrophic denitrification nitrogen removal treatment, the fine particle powder of elemental sulfur used is likely to cause impurities in the effluent and requires multiple filtrations. To solve this problem, currently, the sulfur autotrophic biological filler is made into granular filler after melting and cooling of elemental sulfur to avoid the loss of elemental sulfur with the effluent, but it will still cause acidification of the effluent, and the implementation of the melting and heating process will undoubtedly increase the production cost of the filler, resulting in a higher price.

[0006] In view of this, it is necessary to develop a solid filler for microbial autotrophic denitrification that does not require an external carbon source, has a low cost, can prevent the effluent from being overly acidic, and is suitable for use. Summary of the Invention

[0007] Aiming at the technical problems existing in the background technology, the purpose of the present invention is to provide an autotrophic denitrification nitrogen removal filler suitable for low carbon-nitrogen ratio sewage and its preparation method.

[0008] To achieve the above purpose, the present invention adopts the following technical solutions:

[0009] The first aspect of the present invention provides an autotrophic denitrification nitrogen removal filler suitable for low carbon-nitrogen ratio sewage, which comprises the following raw materials by weight percentage: 40% - 45% of sulfoaluminate cement, 8.5% of silica fume, 1.5% of modified sodium percarbonate, 16.8% - 25.2% of sulfur powder, 16.8% - 25.2% of pyrite powder, and 3% - 8% of calcium carbonate powder.

[0010] Preferably, the purity of the sulfur powder is 95 - 99%, the purity of the pyrite powder is above 85%, and the active oxygen content in the modified sodium percarbonate is 13 - 14%.

[0011] Preferably, the preparation method of the modified sodium percarbonate comprises the following steps:

[0012] Sodium percarbonate is ground into powder and then passed through a 120-mesh sieve to obtain sodium percarbonate powder with a particle size of 120 meshes; gelatinized starch is ground into powder and then passed through a 120-mesh sieve to obtain gelatinized starch powder with a particle size of 120 meshes; manganese dioxide is ground into powder and then passed through a 120-mesh sieve to obtain manganese dioxide with a particle size of 120 meshes;

[0013] The processed sodium percarbonate, gelatinized starch and manganese dioxide powder are uniformly mixed and stored in a mass ratio of 7:2:1 to obtain modified sodium percarbonate.

[0014] The particle sizes of the silica fume, sulfur powder, pyrite powder and calcium carbonate powder are all controlled within the range of 80 to 120 meshes.

[0015] The second aspect of the present invention provides a method for preparing the above-mentioned autotrophic denitrification denitrification filler suitable for low carbon-nitrogen ratio sewage, comprising the following steps:

[0016] S1. Fully mix the raw materials according to the formula to obtain a mixed powder;

[0017] S2, adding water to the mixed powder, stirring evenly to obtain a slurry;

[0018] S3. The slurry is made into particles, and the particles are placed in a ventilated place to dry naturally. After the particles are dried naturally, water is sprayed for curing to further solidify the solid particle material to obtain an autotrophic denitrification filler.

[0019] Preferably, the amount of water added is 20-30 wt % of the total mass of the mixed powder.

[0020] Preferably, the particle size of the particles after natural air drying is 5-8 mm.

[0021] Preferably, the natural air drying time is 20 to 24 hours.

[0022] Preferably, the water spraying curing treatment is: use a watering can to spray water on the surface of the particles, wait for them to dry naturally, and repeat this operation for 3 consecutive days, once a day.

[0023] The present invention has the following beneficial effects:

[0024] (1) The autotrophic denitrification filler provided by the present invention. Selecting calcium sulfoaluminate cement as the binder can ensure the physical strength of the filler. At the same time, the internal alkalinity after its setting is lower than that of Portland cement, and it is easier for microorganisms to grow on the filler. Modified sodium percarbonate is used as the foaming agent, and gas is only generated when water is added, so it is not easy to waste the gas generated by the foaming agent. The gas generated is used to form micropores inside the filler, making it easier for microorganisms to grow on the filler. Adding an appropriate amount of calcium carbonate can provide alkalinity to ensure that the effluent after sulfur autotrophic denitrification will not be overly acidified. Pyrite and sulfur are used as sulfur sources, and through proportioning, sulfur autotrophic denitrifying microorganisms can grow rapidly to initiate the denitrification reaction, while avoiding the acidification of the effluent caused by using only sulfur as the sulfur source. The experimental results show that the autotrophic denitrification filler has excellent denitrification effect on low-concentration nitrate water bodies and can meet the technical requirements of deep denitrification treatment.

[0025] (2) In the present invention, the actual active oxygen of the modified sodium percarbonate is 13 - 14%. When the gelatinized starch is mixed with the modified sodium percarbonate to make the denitrification filler particles, it can form a substance with strong viscosity to slow down the rapid impact of the oxygen generated by the sodium percarbonate when it meets water on the inside of the particles and affect the particle strength. Manganese dioxide acts as a catalyst for the release of oxygen from the sodium percarbonate to ensure that the oxygen contained in the sodium percarbonate can be released completely before the denitrification filler particles solidify their own strength.

[0026] (3) The autotrophic denitrification filler provided by the present invention can simultaneously provide the electron donor sulfur and the alkalinity adjustment buffer during the autotrophic microbial denitrification process. The denitrification process is simple, without the need to use fuel melting raw materials (molten sulfur), and can be applied to large-scale production and actual industrial applications. The microbial biofilm formation is fast, the denitrification efficiency is high, the raw materials are cheap and easy to obtain, the process is simple, and the requirements for equipment / environment are low, saving energy and reducing costs.

[0027] (4) The preparation process of the autotrophic denitrification filler provided by the present invention is simple, and the obtained material has a stable structure. This makes it possible to balance and control the production process and product structure according to different water quality and service life requirements, greatly increasing the scope of application of the product and being easy to promote and apply industrially. Description of the Drawings

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required to be used in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0029] Figure 1 Optical picture of the autotrophic denitrification filler prepared in Example 1;

[0030] Figure 2 Graph of the change in nitrate nitrogen concentration with the number of cycle water replacements during the denitrification performance test of the autotrophic denitrification packing prepared in Example 1;

[0031] Figure 3 Graph of the change in pH with the number of cycle water replacements during the denitrification performance test of the autotrophic denitrification packing prepared in Example 1;

[0032] Figure 4 Graph of the change in nitrate nitrogen concentration with the number of cycle water replacements during the denitrification performance test of the autotrophic denitrification packing prepared in Example 2;

[0033] Figure 5 Graph of the change in pH with the number of cycle water replacements during the denitrification performance test of the autotrophic denitrification packing prepared in Example 2;

[0034] Figure 6 Graph of the change in nitrate nitrogen concentration with the number of cycle water replacements during the denitrification performance test of the molten sulfur autotrophic denitrification packing;

[0035] Figure 7 Graph of the change in pH with the number of cycle water replacements during the denitrification performance test of the molten sulfur autotrophic denitrification packing;

[0036] Figure 8 Graph of the change in nitrate nitrogen concentration with the number of cycle water replacements during the denitrification performance test of the autotrophic denitrification packing prepared in Example 3;

[0037] Figure 9 Graph of the change in pH with the number of cycle water replacements during the denitrification performance test of the autotrophic denitrification packing prepared in Example 3;

[0038] Figure 10 Graph of the change in nitrate nitrogen concentration with the number of cycle water replacements during the denitrification performance test of the autotrophic denitrification packing prepared in Comparative Example 1;

[0039] Figure 11 Graph of the change in pH with the number of cycle water replacements during the denitrification performance test of the autotrophic denitrification packing prepared in Comparative Example 1;

[0040] Figure 12 Graph of the change in nitrate nitrogen concentration with the number of cycle water replacements during the denitrification performance test of the autotrophic denitrification packing prepared in Comparative Example 2;

[0041] Figure 13 Graph of the change in pH with the number of cycle water replacements during the denitrification performance test of the autotrophic denitrification packing prepared in Comparative Example 2;

[0042] Figure 14Graph showing the change in nitrate nitrogen concentration with the number of times of cyclic water replacement during the denitrification performance test of the autotrophic denitrification filler prepared in Comparative Example 3;

[0043] Figure 15 Graph showing the change in pH with the number of times of cyclic water replacement during the denitrification performance test of the autotrophic denitrification filler prepared in Comparative Example 3. Detailed implementation mode

[0044] In the following description, specific details such as specific system structures and technologies are presented for the purpose of illustration rather than limitation, so as to thoroughly understand the embodiments of the present invention. However, those skilled in the art should clearly understand that the present invention can also be implemented in other embodiments without these specific details.

[0045] The present invention provides an autotrophic denitrification filler suitable for low carbon-nitrogen ratio sewage, and its raw materials include the following components by weight percentage: 40% - 45% of sulfoaluminate cement, 8.5% of silica fume, 1.5% of modified sodium percarbonate, 16.8% - 25.2% of sulfur powder, 16.8% - 25.2% of pyrite powder, and 3% - 8% of calcium carbonate powder. Among them, sulfoaluminate cement is used as an adhesive, mainly playing the role of bonding various component substances together; silica fume is used as a physical enhancer, and adding an appropriate amount of silica fume can increase the strength of the filler; modified sodium percarbonate is used as a foaming agent, and it is required that the active oxygen content of the modified sodium percarbonate is 13 - 14%. When the modified sodium percarbonate encounters water, it generates oxygen, which can create small holes inside the filler, increasing the porosity of the filler, and then increasing the specific surface area, making it easier for microorganisms to grow on the filler. The modified sodium percarbonate will decompose to release oxygen and water, and the final reaction product contains sodium carbonate (Na 2 CO 3 )), and the generated sodium carbonate can provide a certain alkalinity to avoid excessive acidity caused by autotrophic denitrification.

[0046] Sulfur powder and pyrite powder are used as the main electron donors for sulfur autotrophic denitrification. The purity of sulfur powder is required to be 95 - 99%, and the purity of iron ore powder is required to be above 85%; calcium carbonate powder is mainly used to provide alkalinity to avoid excessive acidity caused by autotrophic denitrification.

[0047] The particle sizes of silica fume, sulfur powder, pyrite powder, and calcium carbonate powder are all required to be controlled within the range of 80 - 120 mesh.

[0048] Principle of autotrophic denitrification of nitrate nitrogen in water using the autotrophic denitrification packing provided by the present invention: Autotrophic denitrification is carried out using elemental sulfur or pyrite in sulfur-containing substances, enabling nitrate to gain electrons and be reduced to nitrogen gas; during the sulfur autotrophic denitrification process, hydrogen ions are generated as the reaction proceeds, reducing the pH value of the water quality. The sodium carbonate formed by calcium carbonate and foaming agent (modified sodium percarbonate) in the packing provides a certain alkalinity, complementing each other to regulate the acid-base balance of the entire system, thereby achieving the effect of efficient denitrification. The chemical reaction equations involved in the whole process are as follows:

[0049] 55S 0 +20CO 2 +50NO 3 - +38H 2 O+4NH 4 + →4C 5 H 7 O 2 N+55SO 4 2- +25N 2 +64H + (1)

[0050] or 2FeS 2 +6NO 3 - +4H 2 O→3N 2 +4SO 4 2- +2Fe(OH) 3 +2H + (2)

[0051] The alkalinity provided by the sodium carbonate produced from the reaction of calcium carbonate and modified sodium percarbonate in the packing is involved, and the chemical reaction equations are as follows:

[0052] 2H + +CaCO 3 =Ca 2+ +CO 2 +H 2 O (3)

[0053] CO 3 2- +2H + =H 2 O+CO 2 (4)

[0054] Preparation Example

[0055] The preparation method of the modified sodium percarbonate includes the following steps:

[0056] Sodium percarbonate is ground into powder and sieved through a 120-mesh sieve to obtain sodium percarbonate powder with a particle size of 120 mesh; gelatinized starch is ground into powder and sieved through a 120-mesh sieve to obtain gelatinized starch powder with a particle size of 120 mesh; manganese dioxide is ground into powder and sieved through a 120-mesh sieve to obtain manganese dioxide with a particle size of 120 mesh.

[0057] The processed sodium percarbonate, gelatinized starch and manganese dioxide powder are evenly mixed and stored in a mass ratio of 7:2:1 to obtain modified sodium percarbonate.

[0058] Example 1

[0059] A preparation method of an autotrophic denitrification filler applicable to low carbon-nitrogen ratio sewage is as follows:

[0060] S1. Weigh 95% pure sulfur powder (120 mesh), 86% pure pyrite powder (120 mesh), 99.5% pure calcium carbonate powder (120 mesh), ordinary grade 42.5 sulphoaluminate cement, silica fume (120 mesh) and the modified sodium percarbonate in the preparation example according to the weight ratio of 25.2:16.8:3:45:8.5:1.5. The total mass of each raw material is 1 kg, and then they are fully mixed until the colors of each raw material cannot be distinguished to obtain a mixed powder.

[0061] S2. Add 20% of the mass of the mixed powder (water-cement ratio 0.2) of water to the obtained mixed powder, and stir evenly to obtain a slurry.

[0062] S3. After stabilizing the obtained slurry for 1 minute, make it into solid particles with a particle size of 5-8 mm, and then place them in a ventilated place and let them stand and air-dry naturally for 24 hours.

[0063] S4. The naturally air-dried solid particles are subjected to spraying water curing treatment to further solidify. Specifically, use a spray bottle to spray water on the surface of the solid particles and wait for them to air-dry naturally. Repeat this operation 3 days in a row, once a day. After the curing is completed, autotrophic denitrification filler is obtained.

[0064] Example 2

[0065] Weigh 95% pure sulfur powder (120 mesh), 86% pure pyrite powder (120 mesh), 99.5% pure calcium carbonate powder (120 mesh), ordinary grade 42.5 sulphoaluminate cement, silica fume (120 mesh) and the modified sodium percarbonate in the preparation example according to the weight ratio of 25.2:16.8:8:40:8.5:1.5. The total mass of each raw material is 1 kg, and then they are fully mixed until the colors of each raw material cannot be distinguished to obtain a mixed powder; the remaining steps are the same as in Example 1 to obtain autotrophic denitrification filler.

[0066] Example 3

[0067] Sulfur powder (120 mesh) with a purity of 95%, pyrite powder (120 mesh) with a purity of 86%, calcium carbonate powder (120 mesh) with a purity of 99.5%, ordinary grade 42.5 sulphoaluminate cement, silica fume (120 mesh) and modified sodium percarbonate in the preparation example were weighed according to a weight ratio of 16.8:25.2:8:40:8.5:1.5, with a total mass of 1 kg of each raw material, and then fully mixed, with the standard that the color of each raw material cannot be distinguished, to obtain a mixed powder; the remaining steps are the same as in Example 1, to obtain an autotrophic denitrification filler.

[0068] Comparative Example 1

[0069] Sulfur powder (120 mesh) with a purity of 95%, pyrite powder (120 mesh) with a purity of 86%, calcium carbonate powder (120 mesh) with a purity of 99.5%, ordinary grade 42.5 sulphoaluminate cement, silica fume (120 mesh) and modified sodium percarbonate were weighed according to a weight ratio of 5:37:8:40:8.5:1.5, with a total weight of 1 kg, and then fully mixed, with the standard that the colors of the raw materials could not be distinguished, to obtain a mixed powder; the remaining steps were the same as in Example 1 to obtain an autotrophic denitrification filler.

[0070] Comparative Example 2

[0071] Sulfur powder (120 mesh) with a purity of 95%, pyrite powder (120 mesh) with a purity of 86%, calcium carbonate powder (120 mesh) with a purity of 99.5%, ordinary grade 42.5 sulphoaluminate cement, silica fume (120 mesh) and modified sodium percarbonate were weighed in a weight ratio of 37:5:8:40:8.5:1.5, with a total weight of 1 kg, and then fully mixed, with the standard that the colors of the raw materials could not be distinguished, to obtain a mixed powder; the remaining steps were the same as in Example 1 to obtain an autotrophic denitrification filler.

[0072] Comparative Example 3

[0073] According to the weight ratio of 25.2:16.8:8:40:8.5:1.5, sulfur powder (120 mesh) with a purity of 95%, pyrite powder (120 mesh) with a purity of 86%, calcium carbonate powder (120 mesh) with a purity of 99.5%, ordinary grade 42.5 sulphoaluminate cement, silica fume (120 mesh) and ordinary commercially available sodium percarbonate were weighed, purchased from McLean Reagent, item number S830224, and its active oxygen content was 13-14%. The total mass of each raw material was 1 kg, and then fully mixed, with the standard that the color of each raw material could not be distinguished, to obtain a mixed powder; the remaining steps were the same as in Example 1 to obtain an autotrophic denitrification filler.

[0074] Experimental study on denitrification performance of autotrophic denitrification filler

[0075] Take a certain amount of autotrophic denitrification filler for nitrogen removal experiments, and analyze the nitrogen removal ability of each filler through the experimental results.

[0076] (1) Experimental method

[0077] The specific experimental content is as follows: The experimental water is simulated secondary effluent, that is, a certain amount of CH 3 COONa, KNO 3 and KH 2 PO 4 are added to tap water. The water quality characteristics are: the pH is controlled at 7.0 - 7.3, the nitrate nitrogen concentration is about 30 mg / L, the COD concentration is about 45 mg / L, the total phosphorus is about 3.0 mg / L, and the COD:TN is 1.5.

[0078] Respectively take 30 g of the autotrophic denitrification fillers prepared in Examples 1 - 3 and Comparative Examples 1 - 2 and put them into a 250 mL conical flask as the experimental group. At the same time, put the commercially available molten sulfur autotrophic denitrification filler into a 250 mL conical flask as the control group. Add 30 mL of enriched activated sludge to it, and then add the experimental water to the marked line. After sealing the conical flask, place it in a shaker at 60 r / min and shake, controlling the temperature at 30°C ± 1°C. Control the hydraulic retention time to be 4 h, change 200 mL of water each time and add the experimental water to the marked line again. Continuously measure the nitrate nitrogen concentration and pH of the effluent when changing water each time, and the results are shown in Figure 2-13 .

[0079] From Figure 2 the curve of nitrate nitrogen concentration changing with the number of cyclic water changes, it can be seen that the autotrophic denitrification filler prepared in Example 1 has good nitrogen removal performance. After the reaction, the nitrate nitrogen concentration can be reduced to below 3 mg / L, and the removal rate can reach more than 90%.

[0080] From Figure 3 the curve of the number of cyclic water changes and pH changes, it can be seen that the pH of the effluent of the autotrophic denitrification filler prepared in Example 1 gradually stabilizes between 6.6 - 6.9 after the eighth water change and fluctuates. There is a certain acidification compared with the influent water, but it does not drop below 6.5 (when the pH is lower than 6.5, obvious acidification will occur in the effluent, affecting the denitrification of autotrophic denitrifying microorganisms).

[0081] From Figure 4 the curve of nitrate nitrogen concentration changing with the number of cyclic water changes, it can be seen that the autotrophic denitrification filler prepared in Example 2 has good nitrogen removal performance. After the 11th water change, when it operates stably, the nitrate nitrogen removal efficiency can reach 93%, the nitrate nitrogen concentration can be reduced to below 3 mg / L, and after the 7th water change, the autotrophic denitrifying microorganisms adapt to the reaction conditions and start to be able to operate with a high nitrate nitrogen removal rate.

[0082] From Figure 5 the results of the cyclic water change times and pH change curves, it can be seen that the pH of the effluent of the autotrophic denitrification filler prepared in Example 2 has been stably fluctuating around 7, and there is no obvious acidification compared with the influent water. Compared with Example 1, 8% by mass of calcium carbonate provides sufficient alkalinity.

[0083] From Figure 6 the results, it can be seen that the denitrification efficiency of nitrate nitrogen by the molten sulfur autotrophic denitrification filler is about 90% when it is operating stably.

[0084] From Figure 7 the results, it can be seen that as the denitrification rate of nitrate nitrogen by the molten sulfur autotrophic denitrification filler increases, the pH of its effluent will drop below 6.5. Since the optimal pH range for autotrophic denitrifying microorganisms is 6.5 - 8, a pH below 6.5 will affect the denitrification of autotrophic denitrifying microorganisms.

[0085] From Figure 4 Comparing with Figure 6 the results, it can be seen that the autotrophic denitrification filler prepared in Example 2 has a higher adaptation speed of denitrifying microorganisms than the molten sulfur autotrophic denitrification filler. This is reflected in that as the number of water change times increases, the rate of decrease in the effluent nitrate nitrogen concentration is higher than that of the control group, indicating that the pores formed by the gas generated by the modified sodium percarbonate (as a foaming agent) in the filler successfully provide attachment sites for microorganisms, enabling microorganisms to adapt more quickly. At the same time, it is found that the highest denitrification effect of the autotrophic denitrification filler prepared in Example 2 is also higher than that of the molten sulfur autotrophic denitrification filler.

[0086] From Figure 5 Comparing with Figure 7 the results, it can be seen that the effluent of the autotrophic denitrification filler prepared in Example 2 is basically not acidified, while the effluent of the molten sulfur autotrophic denitrification filler is acidified. This is because an appropriate amount of calcium carbonate and modified sodium percarbonate are added to the raw material formula of the autotrophic denitrification filler prepared in Example 2, and the sodium carbonate generated by calcium carbonate and modified sodium percarbonate when they meet water provides sufficient alkalinity, thus preventing the effluent acidification caused by hydrogen ions generated by autotrophic denitrifying microorganisms during the denitrification process.

[0087] In summary, compared with the molten sulfur autotrophic denitrification filler, the autotrophic denitrification filler prepared in Example 2 can better provide a microbial growth environment, can prevent effluent acidification, and has a simple production process without the need to use additional energy, with lower costs.

[0088] From Figure 8It can be seen from the results that the speed of microbial adaptation of the autotrophic denitrification filler prepared in Example 3 is slightly slower, and it can only stabilize to a relatively high nitrate nitrogen removal rate after the 12th and 13th water replacements. After stable operation, the nitrate nitrogen concentration in the effluent is basically above 3 mg / L, and the nitrate nitrogen removal rate is about 89% (lower than 90%). It is slightly lower than the nitrate nitrogen removal rate and the speed of microbial adaptation of the autotrophic denitrification filler prepared in Example 2. The reason is that the proportion of pyrite components in the formula of this example increases, and the autotrophic denitrifying microorganisms need a longer time to adapt in the experiment, and thus the time required to reach a relatively high nitrate nitrogen removal rate is also longer.

[0089] From Figure 9 It can be seen from the results that the pH of the effluent of the autotrophic denitrification filler prepared in Example 3 has been stable and fluctuates around 7, and there is no obvious acidification compared with the influent. This is because when the proportion of calcium carbonate component is 8% at this time, it can ensure the supply of sufficient alkalinity.

[0090] From Figure 10 It can be seen from the curve of nitrate nitrogen concentration changing with the number of circulating water replacements that the nitrate nitrogen removal rate of the autotrophic denitrification filler prepared in Comparative Example 1 is about 86% after the 15th water replacement, and the highest nitrate nitrogen removal rate reaches 89%. While the nitrate nitrogen removal rate of the autotrophic denitrification filler prepared in Example 2 above is close to 90% after the 7th water replacement, and the highest nitrate nitrogen removal rate reaches more than 90%. The reasons for the need for more water replacement times and the decrease in nitrate nitrogen removal rate in Comparative Example 1 are as follows: too much pyrite is used in Comparative Example 1, resulting in too slow adaptation speed of denitrifying microorganisms. Although both pyrite and sulfur are electron donors for autotrophic denitrifying microorganisms, in actual experiments and applications, sulfur is more easily utilized by autotrophic denitrifying microorganisms, and the speed of microbial metabolism and reproduction through it as an electron donor is also faster.

[0091] From Figure 11 It can be seen from the curve of the number of circulating water replacements and pH change that the pH of the effluent of the autotrophic denitrification filler prepared in Comparative Example 1 has been stable and fluctuates around 7, and there is no obvious acidification compared with the influent. This is because in the present invention, calcium carbonate is mainly used to provide alkalinity to prevent the effluent from acidifying due to hydrogen ions generated by autotrophic denitrification. Calcium carbonate with a component proportion of 8% can provide sufficient alkalinity and effectively prevent hydrolysis acidification.

[0092] From Figure 12From the results of the curve of nitrate nitrogen concentration changing with the number of cycle water replacements, it can be seen that the autotrophic denitrification filler prepared in Comparative Example 2 has good denitrification performance. The autotrophic denitrifying microorganisms adapt quickly, and the removal rate reaches 87% at the 8th water replacement; at the 9th water replacement, the nitrate nitrogen removal rate is above 90%, and the nitrate nitrogen concentration can be reduced to below 3 mg / L. Compared with the autotrophic denitrification filler prepared in Comparative Example 1, the autotrophic denitrifying microorganisms prepared in Comparative Example 2 adapt much faster, which is consistent with the fact that sulfur as an electron donor is more easily utilized by autotrophic denitrifying microorganisms. After the 9th water replacement, the nitrate nitrogen removal effect showed obvious fluctuations. Combining the curve of the number of cycle water replacements and the pH change curve (see Figure 13 ), the pH showed obvious fluctuations after the 9th water replacement, with the highest being 6.94 and the lowest being 6.49. When the pH is lower than 6.5, the effluent will be significantly acidified, affecting the denitrification of autotrophic denitrifying microorganisms and reducing the denitrification efficiency, which in turn leads to fluctuations in nitrate nitrogen in the subsequent effluent. The above results show that if the dosage of sulfur components is too high, it will cause serious acidification of the effluent and a decrease in pH, and even affect the denitrification effect.

[0093] In addition, it should be emphasized here that compared with pyrite, the hydrogen ions generated by sulfur used in the present invention in the denitrification principle for removing the same concentration of nitrate nitrogen are much higher than those of pyrite. When the proportion of sulfur is very high, the acidity generated is higher. In Comparative Example 2, only 8% of calcium carbonate is used, which cannot provide sufficient alkalinity.

[0094] Compared with Example 2, the nitrate nitrogen removal rate of the autotrophic denitrification filler prepared in Comparative Example 2 is close to it, and the adaptation speed of autotrophic denitrifying microorganisms is also comparable. However, because the calcium carbonate used in Comparative Example 2 cannot provide sufficient alkalinity, the pH of the effluent in Comparative Example 2 decreases more significantly.

[0095] From Figure 14 the results of the curve of nitrate nitrogen concentration changing with the number of cycle water replacements, it can be seen that the autotrophic denitrification filler prepared in Comparative Example 3 has good denitrification performance. After the 10th water replacement, when it operates stably, the nitrate nitrogen removal efficiency can reach 91.5%, and the nitrate nitrogen concentration can be reduced to below 3 mg / L.

[0096] The overall removal rate of Example 2 is lower. In Example 2, a removal rate of over 92.5% was achieved at the 8th water change. Moreover, the slope of the effluent concentration curve of nitrate nitrogen is smaller than that of Example 2, which reflects that the autotrophic denitrification filler in Comparative Example 3 requires a longer time for microbial adaptation. More deeply, it reflects that modified sodium percarbonate releases oxygen in time with the help of manganese dioxide to create micropores before the filler is solidified, while the gelatinized starch slows down the impact on the interior of the particles, making the micropores uniform and providing more attachment space for microorganisms. However, for traditional sodium percarbonate, due to its slow and erratic release, the number and volume of micropores are less than those of the autotrophic denitrification filler in Example 2. The higher effluent nitrate nitrogen and the fluctuating concentration reflect that the upper limit of the micropore volume of the filler in Comparative Example 3 is insufficient, and some microorganisms are lost with water change.

[0097] From Figure 15 It can be seen from the results of the cyclic water change times and the pH change curve that the effluent pH of Comparative Example 3 fluctuates around 7 and drops to a minimum of 6.79 without obvious acidification. Basically the same as Example 2, in the case of insufficient micropores inside the filler in Comparative Example 3, the number of autotrophic denitrifying microorganisms is less than that of Example 2, and the added calcium carbonate is sufficient to provide alkalinity.

[0098] The present invention is not limited to the above specific embodiments. Those of ordinary skill in the art, starting from the above concepts and without creative labor, can make various transformations, which all fall within the protection scope of the present invention.

Claims

1. An autotrophic denitrification filler suitable for low carbon-nitrogen ratio sewage, characterized in that: The raw materials include the following by weight percentage: 40% to 45% sulphoaluminate cement, 8.5% silica fume, 1.5% modified sodium percarbonate, 16.8% to 25.2% sulphur powder, 16.8% to 25.2% pyrite powder, and 3% to 8% calcium carbonate powder; The active oxygen content in the modified sodium percarbonate is 13-14%; Sodium percarbonate, gelatinized starch and manganese dioxide powder are uniformly mixed and preserved in a mass ratio of 7:2:1 to obtain modified sodium percarbonate.

2. The autotrophic denitrification filler suitable for low carbon-nitrogen ratio sewage according to claim 1, characterized in that: The purity of the sulfur powder is 95-99%, and the purity of the pyrite powder is above 85%.

3. The autotrophic denitrification and denitrification filler suitable for low carbon-nitrogen ratio sewage according to claim 1, characterized in that: The preparation method of the modified sodium percarbonate comprises the following steps: Sodium percarbonate is ground into powder and then passed through a 120-mesh sieve to obtain sodium percarbonate powder with a particle size of 120 mesh; gelatinized starch is ground into powder and then passed through a 120-mesh sieve to obtain gelatinized starch powder with a particle size of 120 mesh; manganese dioxide is ground into powder and then passed through a 120-mesh sieve to obtain manganese dioxide with a particle size of 120 mesh.

4. The autotrophic denitrification filler suitable for low carbon-nitrogen ratio sewage according to claim 1, characterized in that: The particle sizes of the silica fume, sulfur powder, pyrite powder and calcium carbonate powder are all controlled within the range of 80 to 120 meshes.

5. A method for preparing an autotrophic denitrification filler suitable for low carbon-nitrogen ratio sewage as claimed in any one of claims 1 to 4, characterized in that: The following steps are involved: S1. Fully mix the raw materials according to the weight percentage to obtain a mixed powder; S2, adding water to the mixed powder, stirring evenly to obtain a slurry; S3. The slurry is made into particles, and the particles are placed in a ventilated place to dry naturally. After the particles are dried naturally, water is sprayed for curing to further solidify the solid particle material to obtain an autotrophic denitrification filler.

6. The method for preparing the autotrophic denitrification denitrification filler suitable for low carbon-nitrogen ratio sewage according to claim 5, characterized in that: The amount of water added is 20-30wt% of the total mass of the mixed powder.

7. The method for preparing the autotrophic denitrification denitrification filler suitable for low carbon-nitrogen ratio sewage according to claim 5, characterized in that: The particle size of the particles after natural air drying is 5~8mm.

8. The method for preparing the autotrophic denitrification denitrification filler suitable for low carbon-nitrogen ratio sewage according to claim 5, characterized in that: The natural air drying time is 20 to 24 hours; the water spray curing treatment is: use a spray bottle to spray water on the surface of the particles, wait for them to dry naturally, and repeat this operation for 3 consecutive days, once a day.

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