A composite carbon source for removing nitrate in an aquarium system and a preparation method and application thereof

Abstract

The present application relates to the technical field of water treatment, and discloses a composite carbon source for removing nitrate in an aquarium system, a preparation method and application thereof. The components of the composite carbon source include glycerol, slow-release carbon source, zeolite, citrate, vitamin, HEPES and binder. The glycerol and slow-release carbon source in the composite carbon source form synergy, the former can quickly start microbial action and rapidly reduce the concentration of nitrate, and the latter provides long-term support to ensure the sustainability of the degradation effect. The combination not only improves the denitrification efficiency, but also avoids the side effects caused by excessive short-term carbon source. In addition, the glycerol and citrate are synergistic in both chemical and biological aspects: the former is a short-term and rapid energy source, and the latter plays a role in metal buffering and environmental regulation, and both provide good support for efficient denitrification of microorganisms. In combination with the physical and chemical properties of other components, the stability and efficiency of the composite carbon source for denitrification are improved.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, and in particular to a composite carbon source for removing nitrates from aquarium systems, its preparation method, and its application. Background Technology

[0002] The accumulation of nitrates in aquariums primarily originates from fish excrement, uneaten food, and microbial decomposition. The toxicity of nitrates to aquatic animals increases with both nitrate concentration and exposure time. Freshwater animals appear to be more sensitive to nitrates than marine animals. (10mg NO3...) - Nitrate levels of 1 / L (the maximum federal drinking water standard in the United States) can have adverse effects on freshwater invertebrates, fish, and amphibians. Excessive nitrates can negatively impact fish health, affecting their digestive and respiratory systems, and may even lead to disease and death. Therefore, it is necessary to control nitrate concentrations in water. For marine animals, 20 mg NO3... - The maximum level of nitrates is generally acceptable. However, some marine invertebrates are well adapted to low concentrations of nitrates in their early developmental stages. As ammonia and nitrite are removed from aquariums, nitrates accumulate and become increasingly toxic to fish.

[0003] There are three main methods for removing nitrates from aquariums: physical, chemical, and biological. Physical methods primarily involve water changes, which can be cumbersome. Chemical methods involve adding chemical agents to remove nitrates. Biological methods primarily rely on microorganisms to absorb and utilize nitrates. The former two methods are costly and complex, making biological methods the mainstream. In biological methods, nitrate removal mainly occurs through denitrification, which requires a sufficient carbon source to sustain the reaction. However, different carbon sources can cause water turbidity, unpleasant odors, and excessive algae growth. Therefore, a carbon source is needed that can remove nitrates without harming the aquarium organisms or causing significant changes in water quality. Summary of the Invention

[0004] In view of this, the present invention proposes a carbon source that does not cause significant changes in water quality and can remove nitrates, as well as its preparation method and application.

[0005] The technical solution of the present invention is implemented as follows: In a first aspect, the present invention provides a composite carbon source for removing nitrates from an aquarium system, wherein the components of the composite carbon source include glycerol, a slow-release carbon source, zeolite, citrate, vitamins, HEPES and a binder.

[0006] Specifically, the glycerol in the composite carbon source and the slow-release carbon source form a synergy, the former can quickly start microbial action to rapidly reduce the concentration of nitrate, and the latter provides long-term support to ensure the sustainability of the degradation effect. This combination not only improves the denitrification efficiency, but also avoids the side effects caused by excessive carbon source in a short time. The zeolite provides a favorable attachment and habitat for microorganisms; at the same time, its adsorption of pollutants further reduces the concentration of competitive harmful substances in the solution, indirectly promoting the activity of efficient strains including nitrifying bacteria and denitrifying bacteria. Vitamins promote the metabolic activity of microorganisms, thereby more efficiently utilizing glycerol and slow-release carbon source; in addition, vitamins also improve the stability of the overall ecological environment of the fish tank through nutrient supplementation, promoting the diversity of microbial communities. HEPES and citrate control the buffer and heavy metal toxicity problems of the environment respectively, improving the adaptability and sustainability of the carbon source from the perspective of the metabolic environment of microorganisms.

[0007] The key role of glycerol and citrate in the entire composite carbon source system is reflected in the synergy of chemistry and biology: the former is a short-term and rapid energy source, and the latter plays a role in metal buffering and environmental regulation, and both provide good support for efficient denitrification of microorganisms. Combined with the physical and chemical properties of other components, the stability and efficiency of the composite carbon source denitrification are improved.

[0008] In the process of assimilative denitrification, denitrifying bacteria use carbon sources as electron donors to reduce nitrate nitrogen to ammonium nitrogen, and then synthesize nitrogen-containing organic matter such as amino acids and proteins for cell components, realizing the assimilation of nitrogen.

[0009] On the basis of the above technical scheme, preferably, according to the mass fraction 100%, the components of the composite carbon source include glycerol 2%-30%, slow-release carbon source 5%-30%, zeolite 15%-30%, citrate 5%-20%, vitamins 1%-5%, HEPES 0.1%-0.5%, and binder 20%-30%.

[0010] On the basis of the above technical scheme, preferably, the zeolite is a zeolite modified by iron, manganese and chitosan.

[0011] On the basis of the above technical scheme, preferably, the preparation method of the modified zeolite comprises the following steps:

[0012] S1, zeolite pretreatment: after the zeolite raw material is crushed, it is soaked in an acid solution or an alkali solution, and then washed, dried, and calcined at 400-600℃ for 4-6h;

[0013] S2, preparation of Fe 3+ , Mn 2+The metal salt solution is then used to immerse the pretreated zeolite in the metal salt solution and react at 70-90℃ for 2-4 hours. After that, it is washed and dried.

[0014] S3. Place the zeolite treated in step S3 into a chitosan solution, soak for 3-4 hours and then dry it. Then place it into a CTAB solution, soak for 3-4 hours and then dry it.

[0015] Based on the above technical solutions, preferably, in the metal salt solution, the concentration of FeCl3 is 0.2-0.3 mol / L, the concentration of MnCl2 is 0.1-0.2 mol / L; the mass concentration of chitosan solution is 1-2%, and the concentration of CTAB solution is 0.2-0.5 mol / L.

[0016] The above methods can modify zeolite to provide adsorption / reaction sites, while also providing sustained-release functionality and synergistic effects with carbon sources. Specifically, Fe metal ions are introduced onto the zeolite surface. 3+ It can effectively serve as an adsorption site, enhancing the adsorption of phosphate (PO4). 3- ) and nitrate nitrogen (NO 3- The processing capacity of ) is improved by introducing metal ions Mn. 2+ Nitrate nitrogen (NO) can be accelerated through catalysis. 3- The denitrification conversion of nitrogen (N2) to nitrogen gas, especially when used in conjunction with a carbon source under anaerobic conditions.

[0017] Furthermore, by introducing organic functional groups through chitosan and the surfactant CTAB organic modifier, the adsorption capacity of zeolite for hydrophobic organic pollutants can be improved, while also enhancing the biofilm adhesion effect.

[0018] In addition, the synergistic effect of chitosan loading and HEPES can regulate the microbial health environment, purify water bodies, and accelerate the removal of nitrate nitrogen.

[0019] Based on the above technical solutions, preferably, the slow-release carbon source is one or more of polylactic acid, polyadipic acid, ethylene-vinyl acetate resin, polybutylene succinate, polyhydroxybutyrate, and polycaprolactone.

[0020] Specifically, polylactic acid (PLA), polyhydroxybutyrate (PHB), and polycaprolactone (PCL) form the basis for long-term sustained-release, while poly(PGA) and polybutylene succinate (PBS) provide medium-rate sustained-release performance, optimizing the sustained-release profile. The stability of ethylene-vinyl acetate resin (EVA) complements the high-salt, high-oxygen adaptability of PCL, ensuring long-term operation of the material under harsh conditions. The addition of EVA enhances the physical strength of the composite carbon source particles, preventing particle pulverization and premature disintegration, while PLA and PBS provide basic material adhesion and sustained-release properties.

[0021] The selected materials for slow-release carbon source all have good biodegradability, and the degradation products such as lactic acid, succinic acid and acetic acid can be directly used as carbon sources by microorganisms in the aquatic system, without causing secondary pollution. Through the optimization combination of these components, a balance between rapid start-up of denitrification and long-term stable operation can be found, and the adaptability, stability and promotion value of the composite carbon source can be improved.

[0022] On the basis of the above technical scheme, preferably, the binder is one or more of diatomite, gypsum, polyvinyl alcohol, polyethylene glycol and paraffin wax.

[0023] Diatomite has a large specific surface area, can adsorb harmful substances in water and nutrients that promote the growth of algae, reduce the concentration of toxic substances and inhibit the overgrowth of algae, and provide a cleaner and healthier water environment for fish. Its porosity also provides a large number of attachment sites for beneficial microorganisms such as nitrifying bacteria, promotes the reproduction of beneficial microorganisms, and accelerates the nitrogen cycle in the fish tank, converting harmful ammonia nitrogen into relatively harmless nitrate. In addition, diatomite and gypsum also provide good physical binding of particles, improve mechanical strength, and enable carbon source particles to maintain structural stability in water; polyvinyl alcohol (PVA) and polyethylene glycol (PEG) provide excellent molecular-level binding ability and uniformity. PVA, PEG and inorganic materials such as diatomite and gypsum can be biodegraded or non-toxic degraded, ensuring no secondary pollution risk to the aquatic system. All binders are suitable for a variety of aquatic environments with high salinity, high dissolved oxygen, and variable pH, showing good ecological adaptability.

[0024] Through the combination of the above various binders, the dissolution rate of the carbon source particles can be adjusted. For example, paraffin wax provides good coating and slow-release effect, and diatomite and gypsum act as carriers to adjust the release curve of the particles.

[0025] On the basis of the above technical scheme, preferably, the vitamins are one or more of ascorbic acid, riboflavin, nicotinic acid, biotin, pyridoxine and calciferol.

[0026] Specifically, the above-mentioned vitamins support the working efficiency of denitrifying bacteria and nitrifying bacteria from multiple aspects through different promoting effects on microbial metabolism, electron transfer and energy generation. Ascorbic acid can reduce harmful free radicals generated during the denitrification process, thereby maintaining the integrity of the cell structure and function of denitrifying bacteria. Moreover, ascorbic acid indirectly affects the activity of denitrification-related enzymes (such as nitrate reductase and nitrite reductase) by regulating the intracellular redox state, optimizing the progress of the denitrification reaction, and promoting denitrifying bacteria to convert nitrate nitrogen and nitrite nitrogen into nitrogen gas and expel it outside the body. Riboflavin can promote the increase of nitrate reductase in the periplasmic space of the outer membrane of denitrifying bacteria, which is beneficial to improve the denitrification reaction rate and conversion rate, and thus improve the denitrification efficiency of denitrifying bacteria. Riboflavin can enhance the interaction between microorganisms, promote cell aggregation and biofilm formation, which helps denitrifying bacteria to better adhere and survive in the environment, improves their stability and adaptability in complex environments, and thus more effectively plays a denitrification role. Under low temperature and limited carbon source conditions, riboflavin can also regulate the pH of the system, creating an environment suitable for the growth and denitrification of denitrifying bacteria, thereby improving the removal rate of nitrate nitrogen and total nitrogen by denitrifying bacteria.

[0027] Niacin, pyridoxine, etc. help microorganisms maintain reproduction and homeostasis under environmental stress conditions, while ascorbic acid and calciferol improve the overall health of the aquatic system and indirectly improve the tolerance of the bacterial community. The above-mentioned vitamins not only directly promote microbial metabolism, but also indirectly promote the growth and health of aquatic organisms to build a balanced and efficient ecosystem.

[0028] In a second aspect, the present application provides a preparation method of a composite carbon source for removing nitrate in an aquarium system, comprising the following steps:

[0029] S1, uniformly mix glycerol, slow-release carbon source, citrate, vitamin, HEPES, zeolite and binder, then put into a granulator for granulation to obtain a composite carbon source with a particle size of 3-5 mm;

[0030] S2, dry and cool the composite carbon source obtained in step S1 to obtain the finished product.

[0031] In a third aspect, the present application provides the application of the composite carbon source in removing nitrate in the water quality of a fish tank.

[0032] On the basis of the above technical solutions, preferably, the composite carbon source is placed in the water of the fish tank, and BQN2 solid nitrifying bacteria and BP102 solid nitrifying bacteria are added.

[0033] On the basis of the above technical solutions, preferably, the amount of the composite carbon source is 1%-1.5% of the weight of the water in the fish tank.

[0034] On the basis of the above technical scheme, preferably, the amount of the BQN2 solid nitrifying bacteria is 0.1‰-0.5‰ of the weight of the fish tank water, and the amount of the BP102 solid nitrifying bacteria is 0.1‰-0.2‰ of the weight of the fish tank water.

[0035] BQN2 and BP102 solid nitrifying bacteria are both strains developed by the applicant, wherein the BQN2 solid nitrifying bacteria are Bacillus subtilis (CCTCC NO: M 2020551), and the BP102 solid nitrifying bacteria are Bacillus pumilus (CCTCC NO: M 2020550).

[0036] The composite carbon source for removing nitrate in an aquarium system, the preparation method and the application of the composite carbon source have the following beneficial effects relative to the prior art:

[0037] (1) Breaking the traditional denitrification limit: the traditional nitrate removal technology is to realize denitrification under anaerobic or anoxic conditions, and since the dissolved oxygen states of different fish tanks are different, the carbon source combined with the composite denitrifying bacteria can remove nitrate under the condition of 0-5 mg / L of dissolved oxygen.

[0038] (2) Coupling anaerobic denitrification and aerobic assimilation to improve the denitrification efficiency: the composite carbon source can not only provide a suitable biological membrane growth environment and promote the activity of microorganisms, but also couple denitrification and assimilation to fundamentally improve the denitrification efficiency.

[0039] (3) Simplifying the carrier production process flow: the granulation technology and heating technology are coupled to directly form a unique production line, the process flow is simple, the operation is simple, and the limitation of the content of a single raw material of the carrier is avoided.

[0040] (4) The carbon source has strong adaptability, and combined with the composite denitrifying bacteria developed by the company, it can adapt to different water quality and environmental conditions, especially the applicability of high salt and high dissolved oxygen, and the technical popularization is improved. BRIEF DESCRIPTION OF DRAWINGS

[0041] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creating laborious efforts.

[0042] Figure 1 A physical map of the composite carbon source for removing nitrate in an aquarium system prepared by the present application;

[0043] Figure 2 An effect diagram of the composite carbon source prepared by the present application on the pH stability of water;

[0044] Figure 3 Effect diagram of nitrate removal by the composite carbon source prepared in the application. DETAILED DESCRIPTION

[0045] The technical solutions in the embodiments of the application will be clearly and completely described in combination with the embodiments of the application. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the application.

[0046] Example 1

[0047] The components of the composite carbon source in this example include glycerol 30%, polylactic acid 5%, polyadipic acid 18.5%, zeolite 15%, citrate 10%, riboflavin 0.5%, nicotinic acid 0.5%, HEPES 0.5%, gypsum 10% and polyethylene glycol 10%.

[0048] 600 g of the composite carbon source was prepared according to the above proportions. First, 300 g of the mixture was put into a disc granulator, and atomized water was added in batches. The amount of atomized water added at one time was 2% of the weight of the mixture. After the atomized water was added, another 300 g of the mixture was added, and this step was repeated. Through the rotation of the disc, the water and the powdery material were constantly tumbled and agglomerated, and the particles gradually became larger. When the particles in the disc were prepared to 3-5 mm particles, the particles were put into an oven and heated at 130°C for 4 h. After cooling at room temperature, the composite carbon source was obtained by sieving.

[0049] Example 2

[0050] The difference between Example 2 and Example 1 is that the zeolite is a modified zeolite, and the preparation method is as follows:

[0051] S1, zeolite pretreatment: the zeolite raw material was crushed (about 1 mm) and then soaked in a 1 mol / L HCl acid solution (liquid-solid ratio 10:1) at 80°C. Then, it was washed with water until neutral, dried at 80°C, and then calcined at 500°C for 6 h;

[0052] S2, a metal salt aqueous solution containing Fe 3+ and Mn 2+ was configured (FeCl3 0.25 mol / L, MnCl2 0.15 mol / L), and then the pretreated zeolite was immersed in the metal salt solution (liquid-solid ratio 10:1) and stirred at 70°C in a water bath for 4 h. Then, it was washed and dried.

[0053] S3, the zeolite treated in step S3 is placed in a chitosan solution with a mass concentration of 1.5% (prepared with acetic acid with a volume concentration of 1%), and after stirring and soaking for 3h, it is taken out and dried, and then placed in a CTAB (cetyltrimethylammonium bromide) solution with a concentration of 0.4 mol / L, soaked for 4h, and dried.

[0054] Example 3

[0055] The components of the composite carbon source in this example include glycerol 2%, polybutylene succinate 30%, modified zeolite 30%, citrate 5%, ascorbic acid 2.9%, HEPES 0.1%, diatomite 10%, and polyvinyl alcohol 15%.

[0056] The method for preparing the modified zeolite is as follows:

[0057] S1, zeolite pretreatment: the zeolite raw material is crushed (about 1 mm) and then soaked in an 80°C 1 mol / L HCl acid solution or 1 mol / L NaOH base solution (liquid-solid ratio 10:1), and then washed with water until neutral, dried at 80°C, and then calcined at 400°C for 6h;

[0058] S2, an aqueous solution containing metal salts of Fe 3+ and Mn 2+ is prepared (FeCl3 0.2 mol / L, MnCl2 0.2 mol / L), and then the pretreated zeolite is immersed in the metal salt solution (liquid-solid ratio 10:1), stirred and reacted at 70°C in a water bath for 4h, and then washed and dried;

[0059] S3, the zeolite treated in step S3 is placed in a chitosan solution with a mass concentration of 1.5% (prepared with acetic acid with a volume concentration of 1%), and after stirring and soaking for 3h, it is taken out and dried, and then placed in a CTAB (cetyltrimethylammonium bromide) solution with a concentration of 0.4 mol / L, soaked for 4h, and dried.

[0060] 600g of the composite carbon source is prepared according to the above proportions. First, 300g of the mixture is placed in a disc granulator, and atomized water is added in batches, with the amount of atomized water added in each batch being 2% of the weight of the mixture. After the atomized water is added, another 300g of the mixture is added, and this step is repeated. The water and the powdered material are constantly tumbled and agglomerated by the rotation of the disc, and the particles gradually increase in size. When the particles in the disc reach a size of 3-5mm, the particles are placed in an oven and heated at 130°C for 4h. After cooling at room temperature, the composite carbon source is obtained by sieving.

[0061] Example 4

[0062] The components of the composite carbon source of the present embodiment include glycerol 20%, ethylene-vinyl acetate resin 3%, polyhydroxybutyrate 2%, modified zeolite 19.7%, citrate 20%, biotin 2%, pyridoxine 2%, calciferol 1%, HEPES 0.3%, and diatomite 20%, and paraffin 10%.

[0063] The preparation method of the modified zeolite is as follows:

[0064] S1, zeolite pretreatment: after the zeolite raw material is crushed (about 1 mm), it is soaked in a 1 mol / L HCl acid solution or a 1 mol / L NaOH alkali solution (liquid-solid ratio 10:1), then washed with water to neutral, dried at 80°C, and then calcined at 600°C for 4 h;

[0065] S2, a metal salt aqueous solution containing Fe 3+ and Mn 2+ is configured, and then the pretreated zeolite is immersed in the metal salt solution (liquid-solid ratio 10:1), stirred and reacted at 90°C in a water bath for 2 h, then washed and dried;

[0066] S3, the zeolite treated in step S3 is placed in a chitosan solution with a mass concentration of 2% (configured with 1% acetic acid by volume), stirred and soaked for 4 h, then taken out and dried, and then placed in a 0.2 mol / L CTAB (cetyltrimethylammonium bromide) solution, soaked for 4 h, and then dried.

[0067] According to the above proportion, 600 g of the composite carbon source is prepared. First, 300 g of the mixture is placed in a disc granulator, and atomized water is added in batches. The single addition amount of the atomized water is 2% of the weight of the mixture. After the addition of the atomized water, another 300 g of the mixture is added. This step is repeated. Through the rotation of the disc, the water and the powdery material are constantly tumbled and agglomerated, and the particles gradually become larger. When the particles in the disc are prepared to 3-5 mm particles, the particles are placed in an oven and heated at 130°C for 4 h. After cooling at room temperature, the composite carbon source is obtained by sieving.

[0068] Example 5

[0069] The components of the composite carbon source of the present embodiment include glycerol 20%, ethylene-vinyl acetate resin 3%, polyhydroxybutyrate 2%, modified zeolite 19.7%, citrate 20%, biotin 2%, pyridoxine 2%, calciferol 1%, HEPES 0.3%, and diatomite 20%, and paraffin 10%.

[0070] The preparation method of the modified zeolite is as follows:

[0071] S1, Zeolite pretreatment: After crushing the zeolite raw material (about 1 mm), soak it in a 1 mol / L HCl acid solution or a 1 mol / L NaOH alkaline solution at 80℃ (liquid-solid ratio 10:1), then wash it with water until neutral, dry it at 80℃, and then calcine it at 550℃ for 4.5 h.

[0072] S2, configuration containing Fe 3+ Mn 2+ The metal salt aqueous solution (FeCl3 0.2 mol / L, MnCl2 0.1 mol / L) was prepared, and then the pretreated zeolite was immersed in the metal salt solution (liquid-solid ratio 10:1), and the reaction was stirred in a water bath at 75℃ for 3.5 h. After that, it was washed and dried.

[0073] S3. The zeolite treated in step S3 is placed in a chitosan solution with a mass concentration of 1.8% (prepared with acetic acid with a volume concentration of 1%), stirred and soaked for 4 hours, then removed and dried. Then it is placed in a 0.3 mol / L CTAB (hexadecyltrimethylammonium bromide) solution, soaked for 4 hours, and then dried.

[0074] Mix the above materials thoroughly to ensure stable granulation quality. Turn on the disc granulator, place 300g of the mixture into the disc, and add atomized water in batches. The amount of atomized water added at a time is 2% of the weight of the mixture. After adding atomized water, add another 300g of the mixture and repeat this step. The rotation of the disc causes the water and powder to continuously tumble and agglomerate, and the particles gradually become larger. When the particles in the disc reach 3-5mm in size, place the particles in an oven and heat at 130℃ for 4 hours. After cooling at room temperature, sieve to obtain the composite carbon source.

[0075] Example 6

[0076] The composite carbon source in this embodiment comprises 20% glycerol, 5% polylactic acid, 5% polyadipate, 5% ethylene-vinyl acetate resin, 5% polybutylene succinate, 5% polycaprolactone, 15% modified zeolite, 15% citrate, 1% riboflavin, 1% biotin, 1% calciferol, 0.5% HEPES, 6.5% diatomaceous earth, gypsum, 10% polyvinyl alcohol, and 5% paraffin.

[0077] The preparation method of modified zeolite is as follows:

[0078] S1, Zeolite pretreatment: After crushing the zeolite raw material (about 1 mm), soak it in a 1 mol / L HCl acid solution or a 1 mol / L NaOH alkaline solution at 80℃ (liquid-solid ratio 10:1), then wash it with water until neutral, dry it at 80℃, and then calcine it at 450℃ for 5.5 h.

[0079] S2, configuration containing Fe 3+ Mn2+ The pretreated zeolite was immersed in an aqueous solution of metal salts (FeCl30.3 mol / L, MnCl20.2 mol / L), and then the pretreated zeolite was immersed in the metal salt solution (liquid-solid ratio 10:1) and stirred at 85°C in a water bath for 2.5h, and then washed and dried;

[0080] S3, the zeolite treated in step S3 was placed in a chitosan solution with a mass concentration of 1.3% (prepared with 1% acetic acid by volume), and stirred and soaked for 3h, then taken out and dried, and then placed in a CTAB (cetyltrimethylammonium bromide) solution with a concentration of 0.45 mol / L, soaked for 3h, and dried.

[0081] The above materials were mixed and stirred uniformly to ensure stable quality for subsequent granulation. The disc granulator was started, 300g of the mixed material was placed in the disc, and atomized water was added in batches, with the amount of atomized water added in each batch being 2% of the weight of the mixed material. After the addition of atomized water, another 300g of the mixed material was added, and this step was repeated. Through the rotation of the disc, the water and the powdered material were constantly tumbled and agglomerated, and the particles gradually increased in size. When the particles in the disc reached a size of 3-5mm, the particles were placed in an oven and heated at 130°C for 4h. After cooling at room temperature, the composite carbon source was obtained by sieving.

[0082] Comparative Example 1

[0083] Comparative Example 1 is the same as Example 1 except that it lacks propylene glycol.

[0084] Comparative Example 2

[0085] Comparative Example 2 is the same as Example 1 except that it lacks citrate.

[0086] Comparative Example 3

[0087] Comparative Example 3 is the same as Example 2 except that the preparation method of the modified zeolite lacks step S3.

[0088] The composite carbon sources prepared in the examples and comparative examples were respectively taken, and according to a fish tank system of 20L of water, 1 / 100 of the volume of the fish tank of the composite carbon source, i.e. 200g of the composite carbon source, 0.1‰ of BQN2 (2g), 0.1‰ of BP102 (2g), and bacteria culture solution (to 100mg / L of nitrate nitrogen) were added, and the fish tank circulation mode was started. Sampling time: sample was taken every 24h to determine device data, and the determination indexes were: determination of NO 3- -N, NO 2- -N, NH4 + -N, pH, TN indexes.

[0089] Table 1 Performance of composite carbon source

[0090] Tolerable conditions Stable load Example 1 Dissolved oxygen 0-5 mg / L, salinity 30000 mg / L, pH 5.5-6.5 1.0 - 1.5 kgN / m 3 / d]] Example 2 Dissolved oxygen 0-5 mg / L, salinity 30000 mg / L, pH 5.5-6.5 2.5-3.0 kgN / m 3 / d]] Example 3 Dissolved oxygen 0-5 mg / L, salinity 30000 mg / L, pH 5.5-6.5 2.0-3.5 kgN / m 3 / d]] Example 4 Dissolved oxygen 0-5 mg / L, salinity 30000 mg / L, pH 5.5-6.5 2.5-3.5 kgN / m 3 / d]] Example 5 Dissolved oxygen 0-5 mg / L, salinity 30000 mg / L, pH 5.5-6.5 2.1-3.5 kgN / m 3 / d]] Example 6 Dissolved oxygen 0-5 mg / L, salinity 30000 mg / L, pH 5.5-6.5 2.0-4.0 kgN / m 3 / d]] Comparative Example 1 Dissolved oxygen 0-5 mg / L, salinity 30000 mg / L, pH 5.5-6.5 0.3 - 0.5 kgN / m 3 / d]] Comparative Example 2 Dissolved oxygen 0-5 mg / L, salinity 30000 mg / L, pH 5.5-6.5 0.5 - 0.8 kgN / m 3 / d]] Comparative Example 3 Dissolved oxygen 0-5 mg / L, salinity 30000 mg / L, pH 5.5-6.5 1.5-2.0 kgN / m 3 / d]]>

[0091] As shown in Table 1, the composite carbon source of the embodiments 1-6 of the present application can adapt to anaerobic and aerobic environments, and can adapt to a water environment of 30000 mg / L with BQN2 and BP102 nitrifying bacteria, and the stable load reaches 1-4 kgN / m 3 / d, has strong adaptability and nitrate nitrogen removal capacity.

[0092] After the modified zeolite, the stable load is greatly improved, because the modified zeolite improves the removal capacity of nitrate. The stable load will decrease significantly due to the lack of glycerol and citrate in the composite carbon source, because the lack of glycerol leads to the decrease of the rapid response capacity of the denitrification process, and the initial denitrification is delayed. The lack of citrate will inhibit microbial activity, especially in long-term operation due to the deterioration of the metabolic environment, and the cumulative negative impact. The lack of glycerol and citrate will lead to insufficient carbon source supply (imbalance of C / N ratio), which directly limits the denitrification reaction, resulting in the decrease of denitrification efficiency.

[0093] I. Colorimetric test

[0094] According to the 20L water fish tank system, 1 / 100 fish tank volume of composite carbon source is added to each fish tank, that is, 200g of composite carbon source, 0.1 ‰ of BQN2 (2g), 0.1 ‰ of BP102 (2g), and bacteria culture solution (to 100 mg / L nitrate nitrogen) is added, the temperature is controlled to 30℃, 5 pieces of grass gold are put in, the fish tank circulation is turned on, and 0.5g of feed is fed every day. In addition, different carbon sources are added to other groups of fish tanks for experiment, and data is collected and analyzed continuously, and the specific grouping is shown in Table 2.

[0095] Table 2 Colorimetric test grouping conditions

[0096]

[0097] According to HJ 1182-2021 Water Quality Colorimetric Dilution Factor Method for Determining the Change of Water Quality Colorimetric, the color of all groups of carbon sources is white at the beginning of the experiment, the water is transparent and colorless, and the colorimetric value is 0. The detection results of 7 days and 25 days after starting are shown in Table 3.

[0098] Table 3 Water quality change

[0099]

[0100] After 25 days of data follow-up, the colorimetric values of the experimental groups of carbon sources 1-3 have different changes, and the colorimetric value of the experimental group with the composite carbon source has no obvious change. The comparative example 1 will increase the accumulation of amines and incomplete metabolic intermediates due to the lack of glycerol, resulting in a light yellow or turbid feeling of the water quality.

[0101] II. pH test

[0102] According to the 20L water fish tank system, 1 / 100 fish tank volume of composite carbon source is added to each fish tank, i.e. 200g of composite carbon source, 0.1‰ BQN2 (2g), 0.1‰ BP102 (2g), and bacterial culture solution (to 100mg / L nitrate nitrogen) is added, the temperature is controlled to 30°C, 5 grass goldfish are put in, the fish tank is opened for circulation, and 0.5g of feed is fed every day. In addition, different carbon sources are added to other groups of fish tanks for experiments, and the initial pH is adjusted to 7.5 using sodium hydroxide solution and dilute sulfuric acid solution. Data is continuously collected for analysis. The specific grouping is shown in Table 4, and the results are shown in Figure 2 .

[0103] Table 4 Experimental grouping

[0104]

[0105] Figure 2 As shown, the pH of the experimental group using the composite carbon source is stable at 7.5-7.6 after 12 days of experiment, and the pH data of the experimental groups of other carbon sources all have different degrees of rise.

[0106] Comparative Example 1 has a decrease in denitrification rate due to the lack of glycerol, and the accumulation of intermediate alkaline byproducts or heavy metal oxidation products leads to the final alkalinity of the water body (slightly higher pH).

[0107] Comparative Example 2 has a decrease in pH buffering effect of the water body due to the lack of citrate, and is easily affected by other reactions to fluctuate.

[0108] III. Denitrification test

[0109] According to the 20L water fish tank system, 1 / 100 fish tank volume of composite carbon source is added to each fish tank, i.e. 200g of composite carbon source, 0.1‰ BQN2 (2g), 0.1‰ BP102 (2g), and bacterial culture solution (to 100mg / L nitrate nitrogen) is added, the temperature is controlled to 30°C, 5 grass goldfish are put in, the fish tank is opened for circulation, and 0.5g of feed is fed every day. In addition, different carbon sources are added to other fish tanks for experiments, and data is continuously collected for analysis. The specific grouping is shown in Table 5, and the results are shown in Figure 3 .

[0110] Table 5 Experimental grouping

[0111]

[0112] Figure 3As shown, after 16 days of experiment, the carbon sources 1, 2 and 3 have certain carbon release capacity in the early stage, and then are utilized by denitrifying microorganisms to remove nitrate, and with the extension of experimental time, the carbon release capacity decreases, no excess carbon source is released, and the nitrate reduction trend gradually stabilizes; the composite carbon source has stable carbon release capacity, the microorganisms continuously have carbon source utilization, and the nitrate concentration can be continuously reduced.

[0113] If the composite carbon source lacks glycerol and / or citrate, the nitrate removal rate will decrease. The composite carbon source of Comparative Example 1 lacks glycerol, which significantly affects the denitrification rate in the start-up period; the composite carbon source of Comparative Example 2 lacks citrate, which has an adverse effect on long-term operation and water quality stability, especially in complex water bodies or high-load operation, the nitrate removal rate decreases more obviously.

[0114] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A composite carbon source for the removal of nitrate in an aquatic system, characterized in that: The components of the composite carbon source include 2%-30% of glycerol, 5%-30% of slow-release carbon source, 15%-30% of zeolite, 5%-20% of citrate, 1%-5% of vitamin, 0.1%-0.5% of HEPES and 20%-30% of binder, according to a mass fraction of 100%; The zeolite is a zeolite modified by iron, manganese and chitosan, and the preparation method comprises the following steps: S1, zeolite pretreatment: after the zeolite raw material is crushed, it is soaked in an acid solution or an alkali solution, and then washed, dried and calcined at 400-600 ℃ for 4-6 h; S2, a solution containing a metal salt of Fe 3+ , Mn 2+ is prepared, and then the pretreated zeolite is immersed in the solution of the metal salt, reacted at 70-90°C for 2-4h, and then washed and dried; S3, the zeolite treated in step S2 is placed in a chitosan solution, soaked for 3-4 h and then dried, and then placed in a CTAB solution, soaked for 3-4 h and then dried.

2. A composite carbon source for removing nitrate in an aquatic system according to claim 1, characterized in that: In the metal salt solution, the concentration of FeCl3 is 0.2-0.3 mol / L, and the concentration of MnCl2 is 0.1-0.2 mol / L; The mass concentration of the chitosan solution is 1-2%, and the concentration of the CTAB solution is 0.2-0.5 mol / L.

3. A composite carbon source for removing nitrate in an aquarium system as claimed in claim 1, characterized in that: The slow-release carbon source is one or more of polylactic acid, polyadipic acid, ethylene-vinyl acetate resin, polybutylene succinate, polyhydroxybutyrate and polycaprolactone; The binder is one or more of diatomite, gypsum, polyvinyl alcohol, polyethylene glycol and paraffin wax; The vitamin is one or more of ascorbic acid, riboflavin, nicotinic acid, biotin, pyridoxine and calciferol.

4. A method of preparing a composite carbon source for the removal of nitrate in an aquarium system according to any one of claims 1 to 3, characterized in that: The method comprises the following steps: S1, glycerol, slow-release carbon source, citrate, vitamin, HEPES, zeolite and binder are uniformly mixed, and then put into a granulator for granulation to obtain a composite carbon source with a particle size of 3-5 mm; S2, the composite carbon source obtained in step S1 is dried and cooled to obtain a finished product.

5. The composite carbon source according to any one of claims 1-3 for removing nitrate in fish tank water.

6. Use according to claim 5, wherein: The composite carbon source is placed in the fish tank water, and BQN2 solid nitrifying bacteria and BP102 solid nitrifying bacteria are added.

7. Use according to claim 6, wherein: The amount of the composite carbon source is 1%-1.5% of the weight of the fish tank water; the amount of the BQN2 solid nitrifying bacteria is 0.1‰-0.5‰ of the weight of the fish tank water, and the amount of the BP102 solid nitrifying bacteria is 0.1‰-0.2‰ of the weight of the fish tank water.

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