Method for realizing heterotrophic nitrification-aerobic denitrification nitrogen removal of wastewater with low carbon nitrogen ratio

Abstract

The invention relates to the technical field of biological sewage treatment, in particular to a method for realizing heterotrophic nitrification-aerobic denitrification nitrogen removal of wastewater with a low carbon nitrogen ratio. According to the method for realizing heterotrophic nitrification-aerobic denitrification nitrogen removal of the wastewater with the low carbon-nitrogen ratio, an exogenous magnetic field is introduced into a slow-release carbon source system, so that the central magnetic field intensity of an aeration tank is 10-40mT, and the metabolic activity of cellulose degrading bacteria in the system is enhanced and the degradation process of cellulose is promoted by utilizing a magnetic biological effect excited by the magnetic field; the carbon source release efficiency is improved, and the problem of limited carbon release amount of the slow-release carbon source is solved. The enhanced carbon release process effectively increases the carbon nitrogen ratio, provides sufficient organic carbon sources and electron donors for heterotrophic nitrification-aerobic denitrification bacteria, makes the heterotrophic nitrification-aerobic denitrification bacteria have advantages in competition with autotrophic bacteria, further enhances the dominant position of heterotrophic nitrification-aerobic denitrification in the denitrification process without changing other operating parameters, realizes efficient denitrification, and improves the denitrification efficiency. Cost is low, operation is simple, and effect is remarkable.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sewage biological treatment, and particularly relates to a method for realizing heterotrophic nitrification-aerobic denitrification of denitrification of low carbon-nitrogen ratio wastewater. BACKGROUND

[0002] The mixed discharge of a large amount of industrial wastewater and domestic wastewater and the dilution of rainwater in the urban sewage network greatly reduces the organic strength of raw water in sewage treatment plants in China, and presents a low carbon-nitrogen ratio characteristic. The traditional biological denitrification process used in sewage treatment plants cannot obtain sufficient organic carbon to provide an electron donor for denitrification due to the low carbon raw water characteristics, so that the nitrification and denitrification reactions are difficult to reach balance, causing great distress to the total nitrogen discharge of the effluent. Heterotrophic nitrification-aerobic denitrification as a new type of biological efficient denitrification technology utilizes part of the electrons generated by organic carbon metabolism to carry out the ammonia oxidation process under aerobic conditions, and then utilizes the remaining electrons to carry out denitrification, and has high denitrification efficiency and strong impact load resistance. However, the insufficient supply of organic slow-release carbon source brought by low carbon-nitrogen ratio wastewater will lead to the fact that the heterotrophic nitrification-aerobic denitrification bacteria cannot uptake sufficient growth and metabolism energy, so that the effective denitrification of the heterotrophic nitrification-aerobic denitrification bacteria faces great challenges.

[0003] The sewage treatment plant is faced with the serious problem of poor denitrification process removal effect caused by the lack of organic slow-release carbon source. In view of this problem, low-molecular-weight organic compounds such as methanol, ethanol and acetic acid are often used as liquid slow-release carbon sources and are the preferred external slow-release carbon sources for wastewater denitrification. However, the addition of liquid slow-release carbon sources has the disadvantages of high addition cost, difficult addition amount control and fast reaction speed, which makes biomass slow-release carbon sources gradually gain attention due to the advantages of low cost and continuous and stable release. The invention patent with the application number CN202022802737.9 discloses a denitrification sewage treatment device using reed straw and rice straw as slow-release carbon source filler layer to strengthen denitrification, improves the concentration of slow-release carbon source in the water, so as to play the purpose of strengthening the denitrification process. The average removal rate of nitrate nitrogen of the filter in the rural field pilot test is 57.88%. Although the biomass slow-release carbon source can provide slow-release carbon source, the limited carbon release amount makes the effect of improving the carbon-nitrogen ratio and strengthening denitrification not significant when added alone.

[0004] In order to improve the carbon release amount of biomass slow-release carbon source, researchers have improved the preparation of biomass slow-release carbon source. The invention patent with application number CN202210221529.0 modifies the corn cob slow-release carbon source by soaking in NaOH solution, which destroys its surface structure to dissolve cellulose and release more organic slow-release carbon source from hemicellulose. The total nitrogen removal rate of the effluent is 60.71% after 20 days of system operation. The invention patent with application number CN202211236431.9 crushes corn cob, peanut shell, wheat stem and rice husk, and then preheats them. Under the action of a crosslinking agent, the preheated materials are then frozen and molded. The molded filler is cut and placed in a carrier composed of variable chains to form a composite slow-release carbon source. The ammonia nitrogen removal rate of the composite slow-release carbon source is significantly higher than that of a single slow-release carbon source, but it still cannot completely remove ammonia nitrogen.

[0005] Therefore, there is an urgent need for a low-cost and efficient method to realize the reuse of agricultural waste resources while greatly improving the denitrification effect of low-carbon and nitrogen ratio wastewater. SUMMARY

[0006] The present application provides a method for realizing heterotrophic nitrification-aerobic denitrification denitrification of low-carbon and nitrogen ratio wastewater, which solves the above-mentioned problems existing in the prior art.

[0007] The present application provides a method for realizing heterotrophic nitrification-aerobic denitrification denitrification of low-carbon and nitrogen ratio wastewater, which includes the following steps: (1) arranging a static magnetic field generating device around the aeration tank, adjusting the magnetic field strength, and maintaining the static magnetic field strength in the center of the aeration tank in the range of 10-40 mT; (2) filling the slow-release carbon source and inert stones into the porous hollow biochemical balls to prepare slow-release carbon source biochemical balls; (3) throwing the slow-release carbon source biochemical balls into the aeration tank containing low-carbon and nitrogen ratio wastewater for denitrification; (4) under the condition of continuous aeration in the aeration tank, every time the surface of the aeration tank is fished out, an equal amount of newly prepared slow-release carbon source biochemical balls is added to the aeration tank.

[0008] Although cellulose and hemicellulose in slow-release carbon source can be decomposed into soluble organic matter under the action of cellulose-degrading bacteria, the carbon release amount is limited, and the effect of adding the slow-release carbon source alone on improving the carbon-nitrogen ratio of wastewater is not obvious. In the slow-release carbon source system, an external magnetic field is introduced, and the magnetic bioeffect excited by the magnetic field is utilized. A suitable magnetic field strength promotes the growth and reproduction of cellulose-degrading bacteria, so that more extracellular enzymes such as cellulase are secreted, and the decomposition of organic matter such as cellulose and hemicellulose in the slow-release carbon source is accelerated, thereby creating sufficient organic substrate conditions for heterotrophic nitrification-aerobic denitrification bacteria in a low-carbon environment and providing electrons required for nitrification and denitrification. As heterotrophic nitrification-aerobic denitrification bacteria grow fast and have strong competition for oxygen, the denitrification energy efficiency of the organic slow-release carbon source as an electron donor is significantly higher than that of autotrophic bacteria using inorganic matter as an electron donor, so that the autotrophic bacteria are replaced to occupy the dominant position of denitrification, and the heterotrophic nitrification-aerobic denitrification bacteria occupy the advantage in the competition with autotrophic nitrification bacteria, and finally efficient simultaneous nitrification and denitrification is realized under aerobic conditions, so that the total nitrogen removal rate of the whole system is greatly improved.

[0009] According to the method for realizing heterotrophic nitrification-aerobic denitrification of low-carbon-nitrogen-ratio wastewater, the magnetic field strength in the center of the aeration tank is maintained at 10-40 mT. Within this range, the maximum slow-release carbon source release gain can be obtained at a lower energy consumption and equipment cost, and potential inhibition effect or unnecessary cost increase caused by excessive magnetic field can be avoided.

[0010] According to the method for realizing heterotrophic nitrification-aerobic denitrification of low-carbon-nitrogen-ratio wastewater, the static magnetic field is generated by a permanent magnet or an electromagnet.

[0011] According to the method for realizing heterotrophic nitrification-aerobic denitrification of low-carbon-nitrogen-ratio wastewater, the slow-release carbon source is selected from agricultural wastes such as corn cob, straw, sawdust or cotton; the slow-release carbon source is crushed to a particle size of 3-6 mm, and the crushed slow-release carbon source is filled in a porous hollow biochemical ball with a diameter of 45-55 mm and a pore size of less than 3 mm at a weight ratio of 1: (2-3) to the inert stone, so that the overall density of the porous hollow biochemical ball is 1-1.1 g / cm 3 (preferably 1.05 g / cm 3 ), so that the porous hollow biochemical ball can be suspended and rolled by water flow during aeration, so as to be in full contact with the activated sludge.

[0012] In the present application, the design of the porous hollow biochemical ball can effectively prevent the leakage and loss of the 3-6 mm slow-release carbon source particles in the interior, and can ensure that the water flow and microorganisms (such as bacteria) can freely enter and exit for material exchange and biological reaction, which is beneficial to the enrichment and stability of functional bacterial flora.

[0013] The present application selects corn cob, straw and other common agricultural wastes as raw materials, greatly reduces the material cost, realizes the recycling of resources, and meets the requirements of green environmental protection and sustainable development. The raw materials are broken to a particle size of 3-6 mm, which can ensure the sustained and stable release of the slow-release carbon source, and provide sufficient surface for microbial attachment and degradation, ensuring the good matching of the release rate of the slow-release carbon source and the utilization rate of the microorganism. The reaction rate of the oversized particles is slow, and the small particles may be released too quickly or easily lost.

[0014] The method for realizing heterotrophic nitrification-aerobic denitrification of low carbon-nitrogen ratio wastewater according to the present application adopts dry feeding mode to sprinkle the slow-release carbon source biochemical balls in the aeration tank, and the filling volume ratio is 10%-20%.

[0015] Such a filling volume ratio can ensure that sufficient total slow-release carbon source is provided in the aeration tank to meet the denitrification demand, while avoiding affecting the effective volume, hydraulic flow pattern and aeration efficiency of the aeration tank due to excessive filling.

[0016] The filling volume ratio is preferably 12%-18%, and more preferably 15% in the method for realizing heterotrophic nitrification-aerobic denitrification of low carbon-nitrogen ratio wastewater according to the present application.

[0017] The weight ratio of the slow-release carbon source to the inert stone is 1:(2-3), preferably 1:(2-2.5), and more preferably 1:2 in the method for realizing heterotrophic nitrification-aerobic denitrification of low carbon-nitrogen ratio wastewater according to the present application.

[0018] In step (4) of the method for realizing heterotrophic nitrification-aerobic denitrification of low carbon-nitrogen ratio wastewater according to the present application, the dissolved oxygen is controlled at 4.5-5.5 mg / L under the continuous aeration state of the aeration tank, and the floating balls on the surface of the aeration tank are fished out every 10-15 days to ensure that the number of fished balls accounts for 45%-55% of the total number.

[0019] Controlling the dissolved oxygen at 4.5-5.5 mg / L according to the present application creates the most suitable growth and metabolic environment for heterotrophic nitrification-aerobic denitrification bacteria, ensuring that the two key steps of nitrification and aerobic denitrification can be efficiently synchronized. Replacing 45%-55% of the biochemical balls every 10-15 days is an optimal replacement strategy calculated based on the release curve of the slow-release carbon source and the iteration period of the microorganism, which not only can supplement fresh slow-release carbon source in time, but also retains part of the old balls of mature attached microorganisms. These old balls can serve as a seed for the rapid growth of the microbial membrane on the newly added biochemical balls, greatly shortening the start-up time of the new balls and ensuring the smooth transition and continuous high efficiency of the overall efficiency of the system.

[0020] The method for realizing heterotrophic nitrification-aerobic denitrification of low carbon-nitrogen ratio wastewater according to the application, in step (4), the stable heterotrophic nitrification-aerobic denitrification state is reached after replacing 3-4 batches of slow-release carbon source biochemical balls.

[0021] In the method, the low carbon-nitrogen ratio wastewater is fed into the aeration tank every day, and the removal is mainly in the traditional denitrification mode before 3-4 batches, and the heterotrophic nitrification-aerobic denitrification mode is mainly used after 3-4 times, and the total inorganic nitrogen removal rate of the water fed every day is more than 75% after that.

[0022] The method for realizing heterotrophic nitrification-aerobic denitrification of low carbon-nitrogen ratio wastewater according to the application, in the low carbon-nitrogen ratio wastewater, the carbon-nitrogen ratio is 3-4.5, and the abundance of the heterotrophic nitrification-aerobic denitrification bacteria is 5-10%.

[0023] The method for realizing heterotrophic nitrification-aerobic denitrification of low carbon-nitrogen ratio wastewater according to the application, the composition of the low carbon-nitrogen ratio wastewater is that 0.1-0.2 grams of glucose, 0.01-0.03 grams of sodium acetate, 0.02-0.04 grams of starch, 0.1-0.3 grams of ammonium chloride, 0.4-0.6 grams of sodium bicarbonate, 0.01-0.03 grams of potassium dihydrogen phosphate, 0.02-0.04 grams of calcium chloride dihydrate and 0.02-0.04 grams of magnesium chloride hexahydrate are contained in each liter of water, the concentration of the activated sludge is 1000-2000 mg / L, and the carbon-nitrogen ratio is 3-4.5; wherein the initial abundance of the heterotrophic nitrification-aerobic denitrification bacteria in the activated sludge is 5-10%, and the initial abundance of other traditional denitrification bacteria (such as autotrophic nitrification bacteria and anoxic denitrification bacteria) is 50-55% in total.

[0024] The method for realizing heterotrophic nitrification-aerobic denitrification of low carbon-nitrogen ratio wastewater according to the application, the composition of the low carbon-nitrogen ratio wastewater is that 0.1-0.2 grams of glucose, 0.01-0.03 grams of sodium acetate, 0.02-0.04 grams of starch, 0.1-0.3 grams of ammonium chloride, 0.4-0.6 grams of sodium bicarbonate, 0.01-0.03 grams of potassium dihydrogen phosphate, 0.02-0.04 grams of calcium chloride dihydrate and 0.02-0.04 grams of magnesium chloride hexahydrate are contained in each liter of water, the concentration of the activated sludge is 1000-2000 mg / L, and the carbon-nitrogen ratio is 3-4.5; wherein the initial abundance of the heterotrophic nitrification-aerobic denitrification bacteria in the activated sludge is 5-10%, and the initial abundance of other traditional denitrification bacteria (such as autotrophic nitrification bacteria and anoxic denitrification bacteria) is 50-55% in total. The method for realizing heterotrophic nitrification-aerobic denitrification of low carbon-nitrogen ratio wastewater according to the application, the composition of the low carbon-nitrogen ratio wastewater is that 0.1-0.2 grams of glucose, 0.01-0.03 grams of sodium acetate, 0.02-0.04 grams of starch, 0.1-0.3 grams of ammonium chloride, 0.4-0.6 grams of sodium bicarbonate, 0.01-0.03 grams of potassium dihydrogen phosphate, 0.02-0.04 grams of calcium chloride dihydrate and 0.02-0.04 grams of magnesium chloride hexahydrate are contained in each liter of water, the concentration of the activated sludge is 1000-2000 mg / L, and the carbon-nitrogen ratio is 3-4.5; wherein the initial abundance of the heterotrophic nitrification-aerobic denitrification bacteria in the activated sludge is 5-10%, and the initial abundance of other traditional denitrification bacteria (such as autotrophic nitrification bacteria and anoxic denitrification bacteria) is 50-55% in total. BRIEF DESCRIPTION OF DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the present application or the prior art, the drawings required to be used in the following embodiments or prior art description will be briefly introduced. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0026] Figure 1 Figure for the performance of heterotrophic nitrification, autotrophic nitrification, aerobic denitrification and anoxic denitrification after the corn cob slow-release carbon source coupled with 10mT external magnetic field was operated for 40 days in the stable stage in the implementation process of Example 1 of the present application.

[0027] Figure 2 Figure for the performance of heterotrophic nitrification, autotrophic nitrification, aerobic denitrification and anoxic denitrification after the corn cob slow-release carbon source coupled with 40mT external magnetic field was operated for 40 days in the stable stage in the implementation process of Example 2 of the present application. DETAILED DESCRIPTION

[0028] In order to make the objects, technical solutions and advantages of the present application clearer, the technical solutions in the present application will be described clearly and completely below. Obviously, the described embodiments are some embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0029] The sources of raw materials used in the following experimental examples and embodiments are as follows: Low carbon-nitrogen ratio wastewater: from laboratory synthetic wastewater, the composition is 0.17 grams of glucose, 0.02 grams of sodium acetate, 0.03 grams of starch, 0.19 grams of ammonium chloride, 0.5 grams of sodium bicarbonate, 0.02 grams of potassium dihydrogen phosphate, 0.03 grams of calcium chloride dihydrate and 0.03 grams of magnesium chloride hexahydrate per liter of water, the concentration of activated sludge is 1500mg / L, and the carbon-nitrogen ratio is 4.2.

[0030] Activated sludge: from the aeration tank of Beijing Gaobeidian Sewage Treatment Plant, the initial abundance of heterotrophic nitrification-aerobic denitrification bacteria is 10%, the initial abundance of other traditional denitrifying bacteria (such as autotrophic nitrifying bacteria, anoxic denitrifying bacteria, etc.) is 52%, and the initial abundance of bacteria unrelated to denitrification is 38%.

[0031] Porous hollow biochemical balls: commercially available, plastic material.

[0032] Example 1 The present embodiment provides a method for realizing heterotrophic nitrification-aerobic denitrification of low carbon-nitrogen ratio wastewater, which realizes heterotrophic nitrification-aerobic denitrification by coupling corn cob slow-release carbon source with 10mT external magnetic field, and includes the following steps: Step 1: Two permanent magnets are symmetrically arranged around the aeration tank as static magnetic field generating devices, and the magnetic field strength is adjusted to maintain the magnetic field strength at the center of the aeration tank at 10 mT.

[0033] Step 2: Corn cob is selected as a slow-release carbon source, which is crushed to 5 mm particle size particles, and inert stream stones are filled into the porous hollow biochemical balls with a diameter of 50 mm at a weight ratio of 1:3 to prepare slow-release carbon source biochemical balls.

[0034] Step 3: The slow-release carbon source biochemical balls are scattered in the aeration tank by dry throwing, and the filling volume ratio is 15%.

[0035] Step 4: Under the condition of continuous aeration in the aeration tank, the dissolved oxygen is controlled at 4.5-5.5 mg / L, and every 10 days the floating balls on the surface of the aeration tank are fished out to ensure that the number of fished balls accounts for 50% of the total number, and an equal amount of newly prepared slow-release carbon source biochemical balls is added to the aeration tank.

[0036] After continuous operation, the heterotrophic nitrification-aerobic denitrification state is reached after replacing 3 batches, and the slow-release carbon source biochemical balls are continuously replaced to maintain the heterotrophic nitrification-aerobic denitrification efficiency of the aeration tank.

[0037] After detecting, after replacing 3 batches of corn cob slow-release carbon source biochemical balls, the total inorganic nitrogen removal rate of the system reaches 75.31±4.65%. By Figure 1 It can be seen that the heterotrophic nitrification rate is 4.83% higher than the autotrophic nitrification rate, the aerobic denitrification rate of nitrate nitrogen is 36.18% higher than the anoxic denitrification rate, the aerobic denitrification rate of nitrite nitrogen is 36.07% higher than the anoxic denitrification rate, and the heterotrophic nitrification-aerobic denitrification bacteria become the dominant denitrification mode in the system, thereby realizing heterotrophic nitrification-aerobic denitrification of low carbon-nitrogen ratio wastewater, and the abundance of heterotrophic nitrification-aerobic denitrification bacteria in the aeration tank increases from 10.84% to 51.15%.

[0038] Example 2: The embodiment provides a method for realizing heterotrophic nitrification-aerobic denitrification of low carbon-nitrogen ratio wastewater, which realizes heterotrophic nitrification-aerobic denitrification by coupling corn cob slow-release carbon source with 40 mT external magnetic field, and comprises the following steps: Step 1: Two permanent magnets are symmetrically arranged around the aeration tank as static magnetic field generating devices, and the magnetic field strength is adjusted to maintain the magnetic field strength at the center of the aeration tank at 40 mT.

[0039] Step 2: Corn cob is selected as a slow-release carbon source, which is crushed to 5 mm particle size particles, and inert stream stones are filled into the porous hollow biochemical balls with a diameter of 50 mm at a weight ratio of 1:3 to prepare slow-release carbon source biochemical balls.

[0040] Step 3: Using a dry-dispensing method, slowly released carbon source biochemical balls are scattered into the aeration tank, with a filling volume ratio of 15%.

[0041] Step 4: Under continuous aeration in the aeration tank, the dissolved oxygen is controlled at 4.5-5.5 mg / L. Every 10 days, the floats on the surface of the aeration tank are removed, ensuring that the number removed accounts for 50% of the total number. An equal amount of newly prepared slow-release carbon source bio-balls are then added to the aeration tank.

[0042] After continuous operation and replacement of 3 batches, a stable heterotrophic nitrification-aerobic denitrification state is reached. Continue to replace the slow-release carbon source biochemical balls to maintain the heterotrophic nitrification-aerobic denitrification efficiency of the aeration tank.

[0043] Testing showed that after replacing three batches of corn cob slow-release carbon source biochemical balls, the system's total inorganic nitrogen removal rate reached 77.09±3.89%. Figure 2 It can be seen that the heterotrophic nitrification rate is 37.11% higher than the autotrophic nitrification rate, the aerobic denitrification rate of nitrate nitrogen is 61.62% higher than the anoxic denitrification rate, and the aerobic denitrification rate of nitrite nitrogen is 55.75% higher than the anoxic denitrification rate. Heterotrophic nitrification-aerobic denitrification bacteria have become the dominant nitrogen removal mechanism in the system, thus achieving heterotrophic nitrification-aerobic denitrification of nitrogenous wastewater. The abundance of heterotrophic nitrification-aerobic denitrification bacteria in the aeration tank increased from 10.84% ​​to 58.42%.

[0044] Comparative Example 1 This comparative example provides a method for achieving heterotrophic nitrification-aerobic denitrification of wastewater with a low carbon-to-nitrogen ratio. The difference from Example 1 is that in step 1, the magnetic field strength at the center of the aeration tank is maintained at 0mT.

[0045] The total inorganic nitrogen removal rate reached 70.08% according to the test results. However, the autotrophic nitrification rate in the system was 12.92% higher than the heterotrophic nitrification rate, the anoxic denitrification rate of nitrate nitrogen was 3.87% higher than the aerobic denitrification rate, and the anoxic denitrification rate of nitrite nitrogen was 7.81% higher than the aerobic denitrification rate. The traditional nitrogen removal process (autotrophic nitrification-anoxic denitrification) is still the dominant nitrogen removal method, and heterotrophic nitrification-aerobic denitrification nitrogen removal has not been achieved.

[0046] Comparative Example 2 This comparative example provides a method for achieving heterotrophic nitrification-aerobic denitrification of wastewater with a low carbon-to-nitrogen ratio. The difference from Example 1 is that in step 1, the magnetic field strength at the center of the aeration tank is maintained at 100mT.

[0047] The total inorganic nitrogen removal rate reaches 71.44%, but the autotrophic nitrification rate is 19.19% higher than the heterotrophic nitrification rate, the nitrate nitrogen anoxic denitrification rate is 5.11% higher than the aerobic denitrification rate, and the nitrite nitrogen anoxic denitrification rate is 1.81% higher than the aerobic denitrification rate, so the traditional denitrification process (autotrophic nitrification-anoxic denitrification) is still the dominant denitrification mode, and the heterotrophic nitrification-aerobic denitrification denitrification is not achieved.

[0048] Finally, it should be pointed out that: the above examples are only used to illustrate the technical solutions of the present application, but not to limit it; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for heterotrophic nitrification-aerobic denitrification of nitrogen removal from low C / N wastewater, characterized in that, The method comprises the following steps: (1) arranging a static magnetic field generating device around the aeration tank, adjusting the magnetic field intensity to maintain the static magnetic field intensity in the center of the aeration tank in the range of 10-40 mT; (2) filling the slow-release carbon source and inert stones into the porous hollow biochemical balls to prepare slow-release carbon source biochemical balls; (3) scattering the slow-release carbon source biochemical balls in the aeration tank containing low carbon-nitrogen ratio wastewater; (4) under the condition of continuous aeration of the aeration tank, the floating balls on the surface of the aeration tank are taken out every certain period of time, and an equal amount of newly prepared slow-release carbon source biochemical balls is supplemented into the aeration tank.

2. The method of claim 1, wherein the low C / N ratio wastewater is subjected to heterotrophic nitrification and aerobic denitrification. The static magnetic field is generated by a permanent magnet or an electromagnet.

3. The method of heterotrophic nitrification-aerobic denitrification of nitrogen removal of low carbon-nitrogen ratio wastewater according to claim 1 or 2, characterized in that, The slow-release carbon source is selected from agricultural waste including corn cob, straw, sawdust or cotton; the slow-release carbon source is crushed to a particle size of 3-6 mm, and the inert stone is filled in the porous hollow biochemical ball with a diameter of 45-55 mm and a pore size of less than 3 mm at a weight ratio of 1: (2-3), so as to ensure that the overall density of the porous hollow biochemical ball is 1-1.1 g / cm 3 .

4. The process for heterotrophic nitrification-aerobic denitrification of nitrogen removal according to any one of claims 1 to 3, characterized in that, In step (3), the slow-release carbon source biochemical balls are scattered in the aeration tank in a dry throwing manner, and the filling volume ratio is 10%-20%.

5. The process for heterotrophic nitrification-aerobic denitrification of nitrogen removal according to any one of claims 1 to 4, characterized in that, In step (4), under the condition of continuous aeration of the aeration tank, the dissolved oxygen is controlled in the range of 4.5-5.5 mg / L, the floating balls on the surface of the aeration tank are taken out every 10-15 days through cleaning and fishing, and the number of the taken balls accounts for 45%-55% of the total number.

6. The process for heterotrophic nitrification-aerobic denitrification of nitrogen removal according to any one of claims 1 to 5, characterized in that, In step (4), the stable heterotrophic nitrification-aerobic denitrification denitrification state is reached after 3-4 batches of slow-release carbon source biochemical balls are replaced.

7. The process for heterotrophic nitrification-aerobic denitrification of nitrogen removal according to any one of claims 1 to 6, characterized in that, In the low carbon-nitrogen ratio wastewater, the carbon-nitrogen ratio is 3-4.5, and the initial abundance of the heterotrophic nitrification-aerobic denitrification bacteria is 5-10%.

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