Denitrification agent for aquaculture and preparation method thereof

Abstract

The present application relates to the technical field of aquaculture, and particularly relates to a denitrification agent for aquaculture and a preparation method thereof, which comprises the following raw materials in 100% by weight: modified polymeric ferric sulfate 24-26%, iron hydroxide 36-38%, polymeric aluminum ferric silicate 1.5-2%, calcium supplement 3-3.5%, and the rest is maifanite powder. The denitrification agent has a good water improvement effect, and can effectively remove pathogenic bacteria in water for a long time.

Description

Technical Field

[0001] This invention relates to the field of aquaculture technology, and in particular to a denitrifying agent for aquaculture and its preparation method. Background Technology

[0002] The intensive development of aquaculture, while meeting global demand for aquatic products, has also brought serious challenges to water pollution, with ammonia nitrogen exceeding standards being particularly prominent. Ammonia nitrogen mainly originates from the excrement of farmed organisms, the decomposition of uneaten feed, and the improper use of nitrogen-containing fertilizers. Under high-density farming conditions, these nitrogen-containing organic compounds accumulate in large quantities and are converted by microorganisms into non-ionic ammonia (NH3) and ammonium ions (NH4+). 4+ Ammonia nitrogen exists in the form of non-ionic ammonia. The toxicity of non-ionic ammonia increases significantly with rising pH and temperature, posing a direct threat to aquatic animals. Studies have shown that when ammonia nitrogen concentration exceeds 0.02 ppm, fish may exhibit chronic poisoning symptoms, such as gill tissue damage, decreased blood oxygen-carrying capacity, reduced appetite, and stunted growth; concentrations above 0.2 ppm can lead to acute poisoning, causing frantic swimming, convulsions, and even mass mortality. Furthermore, ammonia nitrogen inhibits phytoplankton photosynthesis, disrupts the aquatic ecological balance, increases the risk of pathogenic bacteria growth, and indirectly increases aquaculture costs and the risk of drug residues.

[0003] Currently used denitrification methods include biofilters and activated carbon adsorption, but these methods have limitations in terms of treatment efficiency, operating costs, and maintenance difficulty. Furthermore, microbial remediation technologies (such as nitrifying bacteria and photosynthetic bacteria) gradually oxidize ammonia nitrogen to nitrate through biotransformation, which aligns with ecological governance principles. However, their effectiveness depends on the bacterial reproduction cycle and environmental stability (such as dissolved oxygen and pH), making them difficult to respond quickly to sudden spikes in ammonia nitrogen or water quality deterioration. Therefore, developing efficient and rapid chemical ammonia nitrogen removal agents has become an urgent industry need. These agents typically degrade ammonia nitrogen directly through oxidation, complexation, or ion exchange mechanisms. For example, patent number CN104973686A discloses a method for preparing a solid carbon source for denitrification of aquaculture wastewater, using rice husks and lychee seeds as the main raw materials, which are crushed and mixed to achieve long-term denitrification.

[0004] For example, patent number CN106976973B discloses "a method for denitrification of wastewater, a wastewater denitrifying agent and its preparation method". The method involves surface treatment of inorganic minerals and loading of catalytic metals, followed by environmental domestication of anaerobic ammonia-oxidizing bacteria to obtain a wastewater denitrifying agent, thereby achieving a highly efficient denitrification effect for wastewater.

[0005] However, some pathogenic bacteria in factory recirculating aquaculture systems can affect the health of humans and animals. Therefore, there is an urgent need for a denitrifying agent that can not only achieve efficient removal of ammonia nitrogen but also improve the antibacterial ability of the water. Summary of the Invention

[0006] The purpose of this invention is to provide a denitrifying agent for aquaculture and its preparation method, so as to solve the problems of current denitrifying agents for aquaculture having limited performance, low efficiency and poor antibacterial ability.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] The present invention provides a denitrifying agent for aquaculture, comprising the following raw materials by weight percentage: 24-26% modified polyferric sulfate, 36-38% ferric hydroxide, 1.5-2% polyaluminum ferric silicate, 3-3.5% calcium supplement, and the balance being maifanite powder.

[0009] In some embodiments, the method for preparing the modified polyferric sulfate includes the following steps: mixing and stirring polyferric sulfate, starch-modified polyacrylamide and deionized water until homogeneous to obtain the modified polyferric sulfate.

[0010] Polyferric sulfate (PFS) is an important inorganic polymeric flocculant in the field of water treatment. It has both coagulation and flocculation functions, is free of aluminum, chlorine and toxic substances, and has excellent water purification effect.

[0011] However, current factory-scale recirculating aquaculture systems not only have the problem of high ammonia nitrogen content, but also generate a large number of pathogenic bacteria due to long-term use, posing a threat to the health of humans and animals. Although the coagulation and flocculation effects of polyferric sulfate can effectively improve the aquatic environment, its antibacterial effect is weak and it cannot effectively remove pathogenic bacteria.

[0012] This application modifies polyferric sulfate by using starch-modified polyacrylamide as a modifier. The synergistic combination of the two not only improves the settling ability of polyferric sulfate on suspended matter in water, but also significantly enhances the antibacterial ability of water, effectively removing pathogenic bacteria from the water.

[0013] In some embodiments, the mass ratio of the polyferric sulfate to the starch-modified polyacrylamide is 1:(0.1~0.3).

[0014] In some embodiments, the preparation method of the starch-modified polyacrylamide includes the following steps:

[0015] S1. Under an inert gas atmosphere, 5-chloro-1-pentene and 4,4'-diaminodicyclohexylmethane were added to toluene, followed by triethylamine. The mixture was heated to 50-60°C and stirred at this temperature for 8-12 hours. After the reaction was completed, the mixture was cooled to room temperature, filtered, extracted, and the organic phases were combined. The combined organic phases were then subjected to column chromatography to obtain the compound represented by Formula I.

[0016] (I);

[0017] S2. Under an inert protective gas atmosphere, the compound represented by Formula I from step S1 is mixed with ethanol and cooled to -5~0℃. Nitric acid solution is added dropwise, followed by an aqueous solution of cyanamide. The mixture is heated to reflux and stirred at this temperature for 20~24h. After the reaction is complete, it is cooled to room temperature and subjected to column chromatography to obtain the compound represented by Formula II.

[0018] (II);

[0019] S3. Add oxidized starch to deionized water and heat to 90~100℃ and stir for 20~40 minutes. Then cool to 60~70℃ to obtain gelatinized oxidized starch.

[0020] S4. Mix polyacrylamide, the compound of formula II obtained in step S2, and deionized water and stir until homogeneous. Then add potassium persulfate, heat to 50-70℃ and stir for 5-7 hours. After the reaction is complete, cool to room temperature to obtain modified polyacrylamide.

[0021] S5. Under an inert protective gas atmosphere, the modified polyacrylamide obtained in step S4 is added to the gelatinized oxidized starch obtained in step S3. The mixture is stirred at 60-70℃ for 20-30 min. Then, the pH of the system is adjusted to 1, potassium permanganate is added, and the mixture is stirred at a constant temperature for 2-3 h. After the reaction is completed, the pH of the system is adjusted to neutral, ethanol is added, and the mixture is filtered to obtain the solid product, namely starch-modified polyacrylamide.

[0022] Polyacrylamide is a commonly used flocculant on the market. Patent number CN118479617B discloses a "method for preparing modified polyferric sulfate for treating industrial wastewater". By modifying polyacrylamide with a quaternary ammonium salt structure and then mixing it with polyferric sulfate, the antibacterial ability is improved. However, the sterilization ability of quaternary ammonium salt is relatively limited, and it is easily affected by hard water and organic matter. It has limited effect on microorganisms such as fungi, Mycobacterium tuberculosis, hydrophilic viruses and bacterial spores.

[0023] This application yields an optimized modified polyacrylamide by using specific raw materials. Its structure contains more efficient, broader-spectrum, and less toxic guanidine groups, making it more suitable for factory recirculating aquaculture systems. Furthermore, mixing the modified polyacrylamide with starch to form an aggregate structure containing a network structure not only improves the stability of the denitrifying agent, but also increases the positive charge sites after modifying the polyferric sulfate, thereby improving the flocculation effect.

[0024] In some embodiments, in step S1, the molar ratio of 5-chloro-1-pentene and 4,4'-diaminodicyclohexylmethane is (1~1.2):1.

[0025] In some embodiments, in step S2, the molar ratio of the compound represented by Formula I to cyanamide is 1:(2.8~3.3).

[0026] In some embodiments, in step S4, the mass ratio of polyacrylamide to the compound represented by Formula II is 1:(0.06~0.1).

[0027] In some embodiments, the mass ratio of the modified polyacrylamide in step S5 to the oxidized starch in step S3 is 1:(0.4~0.7).

[0028] In some embodiments, the calcium supplement is any one or more of calcium sulfate dihydrate, calcium dihydrogen phosphate, calcium lactate, calcium carbonate, and calcium chloride.

[0029] In some embodiments, the average particle size of the maifanite powder is 200-300 mesh.

[0030] Another aspect of the present invention provides a method for preparing a denitrifying agent for aquaculture, comprising the following steps: under the condition of ambient humidity <60%, modified polyferric sulfate, ferric hydroxide, polyaluminum ferric silicate, calcium supplement, and maifanite powder are added to a mixing device and stirred evenly to obtain a denitrifying agent.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] (1) This invention uses modified polyferric sulfate, ferric hydroxide and polyaluminum ferric silicate as flocculants, and synergistically uses calcium supplement and maifan stone powder to obtain a denitrifying agent for aquaculture. Ferric hydroxide and polyaluminum ferric silicate have strong adsorption capacity and can effectively adsorb pollutants such as ammonia nitrogen and nitrite. Calcium supplement can adjust the pH value of water and prevent water acidification. Maifan stone powder has a slow-release effect and can stabilize the water environment for a long time. Modified polyferric sulfate and polyaluminum ferric silicate have good coagulation performance, which can promote the sedimentation of pollutants and improve the transparency of water. Modified polyferric sulfate can also more effectively remove pathogenic bacteria in water and is suitable for different water environments.

[0033] (2) The modified polyferric sulfate of the present invention is modified by using starch-modified polyacrylamide as a modifier. The combination of the two not only improves the settling ability of polyferric sulfate on suspended matter in water, but also greatly improves the antibacterial ability of water, effectively removing pathogenic bacteria in water.

[0034] (3) The starch-modified polyacrylamide structure of the present invention contains more efficient, broader-spectrum and low-toxicity guanidine groups, which are more suitable for factory recirculating aquaculture systems. In addition, the modified polyacrylamide is mixed with starch to form an aggregate structure containing a network structure, which not only improves the stability of the denitrifying agent, but also increases the positive charge sites after the polyferric sulfate is modified, thus improving the flocculation effect. Detailed Implementation

[0035] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0036] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0037] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of the invention. Various modifications and variations to the specific embodiments described in this specification are apparent to those skilled in the art without departing from the scope or spirit of the invention. Other embodiments derived from this specification will be apparent to those skilled in the art. This application specification and embodiments are merely exemplary.

[0038] Unless otherwise specified, the post-processing operations described below, such as "extraction", "combining organic phases", "concentration", "column chromatography", "stirring", "filtration", "cooling", and "drying", can be selected by those skilled in the art based on actual conditions, and are not further limited.

[0039] In the following preparation examples and embodiments, oxidized starch was purchased from Zhejiang Yicun Biotechnology Co., Ltd.; polyacrylamide and polyferric sulfate were purchased from Henan Runquan Purification Materials Co., Ltd.; and polyaluminum ferric silicate was purchased from Henan Junfa Chemical Co., Ltd.

[0040] Preparation Example 1

[0041] The preparation method of starch-modified polyacrylamide includes the following steps:

[0042] S1. Under a nitrogen atmosphere, 110 mmol of 5-chloro-1-pentene and 100 mmol of 4,4'-diaminodicyclohexylmethane were added to 500 mL of toluene, followed by the addition of 150 mmol of triethylamine. The mixture was heated to 55 °C and stirred for 11 h. After the reaction was completed, the mixture was cooled to room temperature, filtered, extracted, and the organic phases were combined. The combined organic phases were then subjected to column chromatography to obtain the compound represented by Formula I.

[0043] (I);

[0044] S2. Under a nitrogen atmosphere, 100 mmol of the compound represented by Formula I from step S1 was mixed with 300 mL of ethanol and cooled to -3 °C. 90 mL of a 70 wt% nitric acid solution was added dropwise, followed by 25 g of a 50 wt% cyanamide solution. The mixture was heated to reflux and stirred for 22 h. After the reaction was complete, it was cooled to room temperature and subjected to column chromatography to obtain the compound represented by Formula II.

[0045] (II);

[0046] S3. Add 150g of oxidized starch to 700mL of deionized water, heat to 95℃ and stir for 30min, then cool to 65℃ to obtain gelatinized oxidized starch.

[0047] S4. Mix 300g of polyacrylamide, 24g of the compound shown in Formula II obtained in step S2, and 2.5kg of deionized water and stir until homogeneous. Then add 0.1g of potassium persulfate, heat to 60℃ and stir for 6h. After the reaction is complete, cool to room temperature to obtain modified polyacrylamide.

[0048] S5. Under a N2 atmosphere, 300g of the modified polyacrylamide obtained in step S4 was added to the gelatinized oxidized starch obtained in step S3. The mixture was stirred at 65℃ for 25min. Then, the pH of the system was adjusted to 1, and 150mL of 0.01g / L potassium permanganate aqueous solution was added. The mixture was stirred at a constant temperature for 3h. After the reaction was completed, the pH of the system was adjusted to 7. Ethanol was added and the mixture was filtered to obtain the solid product, namely starch-modified polyacrylamide.

[0049] Preparation Example 2

[0050] The preparation method of starch-modified polyacrylamide includes the following steps:

[0051] S1. Under a nitrogen atmosphere, 220 mmol of 5-chloro-1-pentene and 100 mmol of 4,4'-diaminodicyclohexylmethane were added to 500 mL of toluene, followed by the addition of 150 mmol of triethylamine. The mixture was heated to 55 °C and stirred for 11 h. After the reaction was completed, the mixture was cooled to room temperature, filtered, extracted, and the organic phases were combined. The combined organic phases were then subjected to column chromatography to obtain the compound represented by Formula III.

[0052] (III);

[0053] S2. Add 150g of oxidized starch to 700mL of deionized water, heat to 95℃ and stir for 30min, then cool to 65℃ to obtain gelatinized oxidized starch.

[0054] S3. Mix 300g of polyacrylamide, 24g of the compound shown in Formula III obtained in step S1, and 2.5kg of deionized water and stir until homogeneous. Then add 0.1g of potassium persulfate, heat to 60℃ and stir for 6h. After the reaction is complete, cool to room temperature to obtain modified polyacrylamide.

[0055] S4. Under a N2 atmosphere, 300g of the modified polyacrylamide obtained in step S3 was added to the gelatinized oxidized starch obtained in step S2. The mixture was stirred at 65℃ for 25min. Then, the pH of the system was adjusted to 1, and 15mL of 0.01g / L potassium permanganate aqueous solution was added. The mixture was stirred at a constant temperature for 3h. After the reaction was completed, the pH of the system was adjusted to 7, and ethanol was added. After filtration, the solid product, namely starch-modified polyacrylamide, was obtained.

[0056] Preparation Example 3

[0057] The preparation method of starch-modified polyacrylamide is the same as that in preparation example 1, except that in step S4, the compound represented by formula II is 45g.

[0058] Preparation Example 4

[0059] The preparation method of starch-modified polyacrylamide is the same as that in preparation example 1, except that in step S3, the oxidized starch is 240g.

[0060] Preparation Example 5

[0061] The preparation method of starch-modified polyacrylamide is the same as that in Preparation Example 1, except that the compound represented by Equal Sum of Formula IV is used.

[0062] (IV)

[0063] The compound represented by Formula II is used instead. The compound represented by Formula IV was prepared according to paragraphs

[0030] -

[0032] of the specification CN118479617B.

[0064] Preparation Example 6

[0065] The preparation method of modified polyferric sulfate includes the following steps: 100g of polyferric sulfate, 20g of starch-modified polyacrylamide and 500g of deionized water are mixed and stirred evenly to obtain modified polyferric sulfate.

[0066] Starch-modified polyacrylamide was prepared in Preparation Example 1.

[0067] Preparation Example 7

[0068] The preparation method of modified polyferric sulfate is the same as that of Preparation Example 6, except that the starch-modified polyacrylamide is prepared by Preparation Example 2.

[0069] Preparation Example 8

[0070] The preparation method of modified polyferric sulfate is the same as that of Preparation Example 6, except that the starch-modified polyacrylamide is prepared by Preparation Example 3.

[0071] Preparation Example 9

[0072] The preparation method of modified polyferric sulfate is the same as that in Preparation Example 6, except that the starch-modified polyacrylamide is prepared in Preparation Example 4.

[0073] Preparation Example 10

[0074] The preparation method of modified polyferric sulfate is the same as that of Preparation Example 6, except that the starch-modified polyacrylamide is prepared by Preparation Example 5.

[0075] Preparation Example 11

[0076] The preparation method of modified polyferric sulfate is the same as that in preparation example 6, except that the amount of starch-modified polyacrylamide added is 40g.

[0077] Preparation Example 12

[0078] The preparation method of modified polyferric sulfate is the same as that in preparation example 6, except that an equal mass of polyacrylamide is used instead of starch-modified polyacrylamide.

[0079] Preparation Example 13

[0080] The preparation method of modified polyferric sulfate is the same as that in preparation example 6, except that an equal mass of oxidized starch is used instead of starch to modify polyacrylamide.

[0081] Example 1

[0082] A denitrifying agent for aquaculture, comprising, by weight percentage (100%), the following raw materials: 25% modified polyferric sulfate, 37% ferric hydroxide, 1.8% polyaluminum ferric silicate, 3.2% calcium sulfate dihydrate, with the balance being maifanite powder.

[0083] The modified polyferric sulfate was prepared by Example 6, and the average particle size of the maifanite powder was 300 mesh.

[0084] The preparation method of the denitrifying agent for aquaculture includes the following steps: under an ambient humidity of 40%, modified polyferric sulfate, ferric hydroxide, polyaluminum ferric silicate, calcium sulfate dihydrate, and maifanite powder are added to a mixing device and stirred evenly to obtain the denitrifying agent.

[0085] Example 2

[0086] A denitrifying agent for aquaculture, comprising, by weight percentage (100%), the following raw materials: 24% modified polyferric sulfate, 36% ferric hydroxide, 1.5% polyaluminum ferric silicate, 3% calcium sulfate dihydrate, with the remainder being maifanite powder.

[0087] The modified polyferric sulfate was prepared by Example 6, and the average particle size of the maifanite powder was 300 mesh.

[0088] The preparation method of the denitrifying agent for aquaculture includes the following steps: under an ambient humidity of 40%, modified polyferric sulfate, ferric hydroxide, polyaluminum ferric silicate, calcium sulfate dihydrate, and maifanite powder are added to a mixing device and stirred evenly to obtain the denitrifying agent.

[0089] Example 3

[0090] A denitrifying agent for aquaculture, comprising, by weight percentage (100%), the following raw materials: 26% modified polyferric sulfate, 38% ferric hydroxide, 2% polyaluminum ferric silicate, 3.5% calcium sulfate dihydrate, with the balance being maifanite powder.

[0091] The modified polyferric sulfate was prepared by Example 6, and the average particle size of the maifanite powder was 300 mesh.

[0092] The preparation method of the denitrifying agent for aquaculture includes the following steps: under an ambient humidity of 40%, modified polyferric sulfate, ferric hydroxide, polyaluminum ferric silicate, calcium sulfate dihydrate, and maifanite powder are added to a mixing device and stirred evenly to obtain the denitrifying agent.

[0093] Example 4

[0094] A denitrifying agent for aquaculture and its preparation method are described. The specific implementation method is the same as in Example 1, except that the modified polyferric sulfate is prepared in Preparation Example 7.

[0095] Example 5

[0096] A denitrifying agent for aquaculture and its preparation method are described. The specific implementation method is the same as in Example 1, except that the modified polyferric sulfate is prepared in Preparation Example 8.

[0097] Example 6

[0098] A denitrifying agent for aquaculture and its preparation method are described. The specific implementation method is the same as in Example 1, except that the modified polyferric sulfate is prepared in Preparation Example 9.

[0099] Example 7

[0100] A denitrifying agent for aquaculture and its preparation method are described. The specific implementation method is the same as in Example 1, except that the modified polyferric sulfate is prepared in Preparation Example 10.

[0101] Example 8

[0102] A denitrifying agent for aquaculture and its preparation method are described. The specific implementation method is the same as in Example 1, except that the modified polyferric sulfate is prepared in Preparation Example 11.

[0103] Example 9

[0104] A denitrifying agent for aquaculture and its preparation method are described. The specific implementation method is the same as in Example 1, except that the modified polyferric sulfate is prepared in Preparation Example 12.

[0105] Example 10

[0106] A denitrifying agent for aquaculture and its preparation method are described. The specific implementation method is the same as in Example 1, except that the modified polyferric sulfate is prepared by Example 13.

[0107] Example 11

[0108] A denitrifying agent for aquaculture and its preparation method are described. The specific implementation method is the same as in Example 1, except that the average particle size of the maifanite powder is 400 mesh.

[0109] Comparative Example 1

[0110] A denitrifying agent for aquaculture and its preparation method are disclosed. The specific implementation method is the same as in Example 1, except that an equal amount of polyferric sulfate is used instead of modified polyferric sulfate.

[0111] Performance testing:

[0112] (1) This experiment was conducted at a fish farm in Guangzhou. The ponds were all 6 mu in size with an average water surface area and a 1 m average depth in the surrounding ditch. Grass carp were the main species raised in the ponds. When the pond water was turbid, the bottom was poor, and foam appeared on the surface of the ponds from time to time, the agents of each example and comparative example were added to 12 of the ponds at a dosage of 300 g / mu. The untreated ponds served as blank controls. The COD value, transparency, nitrite and ammonia nitrogen content of the water were tested 2 days after the treatment.

[0113] (2) Take 500 mL of pond water from 12 groups of the same batch from a certain aquaculture farm in Guangzhou and put them into beakers. Add 15 wt% of the denitrifying agent of each example and comparative example, stir well, and test the antibacterial rate of Escherichia coli and Staphylococcus aureus after 15 days:

[0114] Antibacterial rate (%) = (Number of bacteria in the initial pool water - Number of bacteria in the pool water after adding denitrifying agent) / Number of bacteria in the pool water × 100%.

[0115] The denitrifying agents prepared in the above embodiments and comparative examples were tested according to the above methods (1)-(2), and the test results are shown in Table 1.

[0116] Table 1

[0117]

[0118] Analysis of the data in Table 1 shows that the denitrifying agents prepared in Examples 1-3 have good ammonia nitrogen removal effects and can effectively reduce suspended solids and bacterial content in water. In Example 4, the change in the molar ratio of 5-chloro-1-pentene and 4,4'-diaminodicyclohexylmethane not only affected the antibacterial ability but also reduced the ability to encapsulate suspended solids due to the enhanced network structure. In Example 5, the change in the mass ratio of the compound shown in Formula II to polyacrylamide significantly increased the structural rigidity of the modified polyferric sulfate, making it more difficult to bend the molecular chains and reducing its ability to encapsulate particulate matter. In Example 6, the change in the mass ratio of modified polyacrylamide and oxidized starch also significantly increased the structural rigidity of the modified polyferric sulfate, reducing its ability to encapsulate particulate matter. In Example 7, the use of the compound shown in Formula IV instead of the compound shown in Formula II resulted in… The decreased resistance to hard water led to a slight decrease in antibacterial ability. In Example 8, the change in the mass ratio of polyferric sulfate and starch-modified polyacrylamide resulted in a significant increase in the structural rigidity of the modified polyferric sulfate, reducing its ability to encapsulate particulate matter, but slightly increasing its antibacterial ability. In Example 9, the use of an equal mass of polyacrylamide instead of starch-modified polyacrylamide led to a decrease in the antibacterial ability of the denitrifying agent, as well as a decrease in its adsorption capacity for suspended solids. In Example 10, the use of an equal mass of oxidized starch instead of starch-modified polyacrylamide led to a decrease in both the antibacterial ability and ammonia nitrogen removal capacity of the denitrifying agent. In Example 11, the change in the average particle size of the maifanite powder caused slight agglomeration of the maifanite powder, reducing the release capacity of the effective components and affecting the performance of the denitrifying agent. In Comparative Example 1, the use of an equal amount of polyferric sulfate instead of modified polyferric sulfate affected the performance of the denitrifying agent.

[0119] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A denitrifying agent for aquaculture, characterized in that, The raw materials include the following: modified polymeric ferric sulfate 24-26%, iron hydroxide 36-38%, polymeric aluminum-iron silicate 1.5-2%, calcium supplement 3-3.5%, and the rest is maifanite powder; The preparation method of the modified polymeric ferric sulfate comprises the following steps: mixing, stirring and uniformly mixing polymeric ferric sulfate, starch modified polyacrylamide and deionized water to obtain the modified polymeric ferric sulfate. The preparation method of the starch modified polyacrylamide comprises the following steps: S1, under the atmosphere of inert gas, 5-chloro-1-pentene and 4, 4'-diamino dicyclohexyl methane are added into toluene, then triethylamine is added, the temperature is raised to 50-60 DEG C, constant temperature stirring is carried out for 8-12 h, after the reaction is completed, the temperature is cooled to room temperature, filtration, extraction, the organic phase is combined, and column chromatography is carried out to obtain the compound shown in formula I （Ⅰ）； S2, under the atmosphere of inert protective gas, the compound shown in formula I in step S1 and ethanol are mixed and cooled to-5-0 DEG C, nitric acid solution is added dropwise, then cyanamide aqueous solution is added, the temperature is raised to reflux state, constant temperature stirring is carried out for 20-24 h, after the reaction is completed, the temperature is cooled to room temperature, column chromatography is carried out, and the compound shown in formula II is obtained (Ⅱ)； S3, oxidized starch is added into deionized water, the temperature is raised to 90-100 DEG C, constant temperature stirring is carried out for 20-40 min, then the temperature is cooled to 60-70 DEG C, and the gelatinized oxidized starch is obtained S4, polyacrylamide, the compound shown in formula II obtained in step S2 and deionized water are mixed and stirred uniformly, then potassium persulfate is added, the temperature is raised to 50-70 DEG C, constant temperature stirring is carried out for 5-7 h, after the reaction is completed, the temperature is cooled to room temperature, and the modified polyacrylamide is obtained S5, under the atmosphere of inert protective gas, the modified polyacrylamide obtained in step S4 is added into the gelatinized oxidized starch obtained in step S3, stirring is carried out at 60-70 DEG C for 20-30 min, then the pH of the system is adjusted to 1, potassium permanganate is added, constant temperature stirring is continued for 2-3 h, after the reaction is completed, the pH of the system is adjusted to neutral, ethanol is added, filtration is carried out, and the solid product, i.e. the starch modified polyacrylamide, is obtained.

2. The nitrogen removal agent for aquaculture according to claim 1, characterized by, In step S1, the molar ratio of 5-chloro-1-pentene and 4, 4'-diamino dicyclohexyl methane is (1-1.2):

1.

3. The nitrogen removal agent for aquaculture according to claim 1, characterized by, In step S2, the molar ratio of the compound shown in formula I and cyanamide is 1:(2.8-3.3).

4. The nitrogen removal agent for aquaculture according to claim 1, characterized by, In step S4, the mass ratio of polyacrylamide and the compound shown in formula II is 1:(0.06-0.1).

5. The nitrogen removal agent for aquaculture according to claim 1, characterized by, In step S5, the mass ratio of the modified polyacrylamide and the oxidized starch in step S3 is 1:(0.4-0.7).

6. The nitrogen removal agent for aquaculture according to claim 1, characterized by, The calcium supplement is any one or more of calcium sulfate dehydrate, calcium phosphate dibasic, calcium lactate, calcium carbonate and calcium chloride.

7. The nitrogen removal agent for aquaculture according to claim 1, characterized by, The average particle size of the maifanite powder is 200-300 meshes.

8. A method for producing the nitrogen removal agent for aquaculture according to any one of claims 1 to 7, characterized by, The preparation method comprises the following steps: under the condition that the environmental humidity is less than 60%, the modified polymeric ferric sulfate, iron hydroxide, polymeric aluminum-iron silicate, calcium supplement, maifanite powder are added into a mixing device and stirred uniformly to obtain the denitrification agent.

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