A method for denitrification of high-sulfate high-nitrogen wastewater

Abstract

The present application relates to wastewater biological treatment technical field, disclose a kind of high sulphate high nitrate nitrogen wastewater denitrification processing method, comprising the following steps: (1) in anoxic zone I, anoxic zone II and aerobic zone are filled into biological membrane carrier, and the biological membrane carrier of anoxic zone I and anoxic zone II is attached with salt-tolerant anoxic denitrifying bacteria, and the biological membrane carrier of aerobic zone is attached with salt-tolerant aerobic denitrifying bacteria;(2) the carbon-nitrogen ratio of wastewater to be treated is adjusted to 1.25~1.5, then into anoxic zone I, and carries out first-stage anoxic biological treatment;(3) the effluent of anoxic zone I is introduced into anoxic zone II, and carries out secondary anoxic biological treatment;(4) the effluent of anoxic zone II is introduced into aerobic zone, and carries out aerobic biological treatment.The method of the present application can better utilize denitrifying bacteria to inhibit the enrichment of sulfate-reducing bacteria, avoid the production of toxic sulfide and hydrogen sulfide, thereby improving the efficiency of wastewater denitrification.

Description

Technical Field

[0001] This invention relates to the field of wastewater biological treatment technology, and in particular to a method for denitrification treatment of wastewater with high sulfate and high nitrate nitrogen. Background Technology

[0002] The discharge of nitrate-rich wastewater poses a significant threat to the ecological environment and human health. Therefore, nitrate concentration is a crucial indicator for wastewater quality monitoring, and reducing nitrate concentration in wastewater is a hot research topic in the field of wastewater treatment. Compared to physical and chemical methods, biological denitrification is safe, reliable, environmentally friendly, and can be applied on a large scale, making it the preferred method for wastewater denitrification.

[0003] Industrial processes often generate large quantities of wastewater with high sulfate and high nitrate nitrogen levels. Under anaerobic or anoxic conditions containing organic matter, wastewater with high sulfate concentrations promotes the accumulation of sulfate-reducing bacteria. The metabolic activities of these bacteria produce toxic sulfides and hydrogen sulfide, inhibiting the growth and metabolic activities of other microorganisms, thus leading to poor biological denitrification. Existing wastewater treatment processes for high sulfate and high nitrate nitrogen levels cannot address the problem of sulfides inhibiting denitrifying microorganisms.

[0004] For example, patent CN201910764627.7 discloses a device and method for deep denitrification of sulfate-containing natural rubber processing wastewater. First, hydrogen sulfide and methane are generated in anaerobic methanogenic reactors #1 and #2, and then fed into a PDA reactor along with reflux nitrified liquid for short-cut denitrification and anaerobic ammonium oxidation. The wastewater then enters a nitrification reactor for conventional nitrification. The resulting nitrified liquid, along with H2S and CH4 generated in anaerobic methanogenic reactor #1, enters the denitrification reactor, where nitrate nitrogen is reduced to nitrogen gas and H2S is oxidized to sulfate. In this patent, the hydrogen sulfide generated in the anaerobic methanogenic reactor inhibits subsequent anaerobic ammonium oxidation, nitrification, and denitrification processes, negatively impacting the wastewater denitrification effect. Summary of the Invention

[0005] To address the technical problem of sulfate-reducing bacteria accumulation and subsequent inhibition of biological denitrification caused by sulfate in wastewater, this invention provides a denitrification treatment method for high-sulfate and high-nitrate wastewater. This method effectively utilizes denitrifying bacteria to inhibit the accumulation of sulfate-reducing bacteria, avoiding the generation of toxic sulfides and hydrogen sulfide, thereby improving wastewater denitrification efficiency.

[0006] The specific technical solution of this invention is as follows:

[0007] A method for denitrification treatment of high sulfate and high nitrate nitrogen wastewater includes the following steps:

[0008] (1) Biofilm carriers are filled into the anoxic zone I, anoxic zone II and aerobic zone. Salt-tolerant hypoxic denitrifying bacteria are attached to the biofilm carriers in the anoxic zone I and anoxic zone II, and salt-tolerant aerobic denitrifying bacteria are attached to the biofilm carriers in the aerobic zone.

[0009] (2) Adjust the carbon-nitrogen ratio of the wastewater to be treated to 1.25-1.5, and then pass it into the anoxic zone I for primary anoxic biological treatment; (3) Pass the effluent from the anoxic zone I into the anoxic zone II for secondary biological anoxic treatment.

[0010] (4) The effluent from the anoxic zone II is introduced into the aerobic zone for aerobic biological treatment.

[0011] Denitrifying bacteria can inhibit sulfate-reducing bacteria to a certain extent. Based on this, the present invention uses a biofilm carrier with salt-tolerant aerobic and aerobic denitrifying bacteria attached, combined with anoxic-anoxic-aerobic three-stage biological treatment, which can better utilize denitrifying bacteria to inhibit the activity of sulfate-reducing bacteria, thereby avoiding the inhibition of microbial activity due to the production of toxic sulfides and hydrogen sulfide, and improving the removal efficiency of nitrate nitrogen and organic matter in wastewater.

[0012] Furthermore, denitrification requires a significant carbon source, and appropriately increasing the carbon-to-nitrogen ratio (C / N ratio) can promote denitrification. However, increasing the C / N ratio can also lead to an increase in COD in the treated wastewater. Therefore, this invention incorporates an aerobic zone downstream of anoxic zones I and II, enabling better carbon reduction through aerobic biological treatment and significantly lowering the organic matter content in the wastewater. Moreover, before introducing the wastewater into anoxic zone I, the C / N ratio must be strictly controlled. Maintaining the C / N ratio within the range of 1.25–1.5 achieves high denitrification efficiency while preventing excessively high COD in the treated wastewater.

[0013] Compared to aerobic denitrification, anoxic denitrification is more efficient. Therefore, by carrying out two-stage anoxic biological treatment through anoxic zone I and anoxic zone II, the denitrification effect can be improved and the wastewater treatment time can be shortened.

[0014] Preferably, in step (2), when the carbon-to-nitrogen ratio of the wastewater to be treated is less than 1.25 to 1.5, methanol is added to adjust the carbon-to-nitrogen ratio to 1.25 to 1.5.

[0015] Preferably, in step (2), the hydraulic residence time in the anoxic zone I is 12 to 15 hours.

[0016] Preferably, in step (3), the hydraulic residence time in the anoxic zone II is 12 to 15 hours.

[0017] Preferably, in step (4), the hydraulic retention time in the aerobic zone is 12 to 24 hours.

[0018] Using the above-mentioned treatment time allocation in the anoxic zone I, anoxic zone II, and aerobic zone is beneficial to achieving better denitrification and carbon reduction effects with a shorter wastewater treatment time.

[0019] Preferably, in steps (2) and (3), the dissolved oxygen concentration of the wastewater in anoxic zone I and anoxic zone II is controlled at 0.2 to 0.5 mg / L, and the temperature is controlled at 23 to 27°C.

[0020] Preferably, in step (4), the dissolved oxygen concentration of the wastewater in the aerobic zone is controlled at 7.0 to 8.0 mg / L, and the temperature is controlled at 23 to 27℃.

[0021] By using the above-mentioned dissolved oxygen concentration and temperature settings in the anoxic zone I, anoxic zone II, and aerobic zone, the activity of denitrifying bacteria and their inhibitory effect on sulfate-reducing bacteria can be ensured, achieving high efficiency in both anoxic and aerobic denitrification. At the same time, it can also improve the removal effect of residual organic matter in wastewater in the aerobic zone.

[0022] Preferably, in step (2), a phosphorus source is added to the wastewater before introducing the anoxic zone I, with an addition amount of 0.3 to 0.6 mg / L.

[0023] Preferably, in step (1), the filling volume of the biofilm carrier in the anoxic zone I, anoxic zone II and aerobic zone is 60-70% of the effective volume.

[0024] Preferably, in step (1), the biofilm carrier is composed of a combined packing material and biological ropes, and the specific surface area of ​​the combined packing material is 300-350 m². 2 / m 3 The specific surface area of ​​the bio-rope is 330–400 m². 2 / m 3 .

[0025] Furthermore, the composite filler is composed of plastic rings with a diameter of 80-120 mm and aldehyde-based fibers; the bio-rope is a radial structure composed of elastic material filaments and soft material fibers, with a diameter of 70-90 mm.

[0026] Compared with the prior art, the present invention has the following advantages:

[0027] (1) The present invention uses a biofilm carrier with salt-tolerant aerobic and non-aerobic denitrifying bacteria attached, combined with anoxic-anoxic-aerobic three-stage biological treatment, which can effectively utilize denitrifying bacteria to inhibit the accumulation of sulfate-reducing bacteria, avoid the generation of toxic sulfides and hydrogen sulfide, thereby improving the denitrification efficiency of wastewater.

[0028] (2) The present invention adopts a three-stage biological treatment of anoxic-anoxic-aerobic and controls the carbon-nitrogen ratio of wastewater within a specific range, which can achieve high denitrification efficiency while avoiding excessive COD of wastewater after denitrification treatment.

[0029] (3) By adopting a reasonable treatment time allocation in the anoxic zone I, anoxic zone II and aerobic zone, and controlling the dissolved oxygen concentration and temperature of wastewater in each zone within a specific range, the present invention can further improve the efficiency of denitrification and carbon reduction. Detailed Implementation

[0030] The present invention will be further described below with reference to embodiments.

[0031] General Implementation Examples

[0032] A method for denitrification treatment of high sulfate and high nitrate nitrogen wastewater includes the following steps:

[0033] (1) Salt-tolerant denitrifying sludge is added to the anoxic zone I, anoxic zone II and aerobic zone filled with biofilm carriers. The salt-tolerant denitrifying sludge contains salt-tolerant aerobic and non-aerobic denitrifying bacteria. It is acclimatized and biofilm attached using an acclimatization culture solution containing sulfate and nitrate nitrogen.

[0034] (2) Adjust the carbon-nitrogen ratio of the wastewater to be treated to 1.25-1.5, and then pass it into the anoxic zone I for primary anoxic biological treatment; (3) Pass the effluent from the anoxic zone I into the anoxic zone II for secondary biological anoxic treatment.

[0035] (4) The effluent from the anoxic zone II is introduced into the aerobic zone for aerobic biological treatment.

[0036] In one specific implementation, in step (2), when the carbon-nitrogen ratio of the wastewater to be treated is less than 1.25 to 1.5, methanol is added to adjust the carbon-nitrogen ratio to 1.25 to 1.5.

[0037] In one specific implementation, in step (2), the hydraulic residence time in the anoxic zone I is 12-15h; in step (3), the hydraulic residence time in the anoxic zone II is 12-15h; and in step (4), the hydraulic residence time in the aerobic zone is 12-24h.

[0038] As a specific implementation method, in steps (2) and (3), the dissolved oxygen concentration of wastewater in anoxic zone I and anoxic zone II is controlled at 0.2 to 0.5 mg / L and the temperature is controlled at 23 to 27°C; in step (4), the dissolved oxygen concentration of wastewater in aerobic zone is controlled at 7.0 to 8.0 mg / L and the temperature is controlled at 23 to 27°C.

[0039] In one specific implementation, in step (2), before introducing the anoxic zone I, a phosphorus source is added to the wastewater at a concentration of 0.3 to 0.6 mg / L.

[0040] In one specific implementation, in step (1), the filling volume of the biofilm carrier in the anoxic zone I, anoxic zone II and aerobic zone is 60-70% of the effective volume.

[0041] In one specific embodiment, in step (1), the biofilm carrier is composed of a composite packing material and bio-ropes; the composite packing material is composed of plastic rings with a diameter of 80-120 mm and aldehyde-based fibers, with a specific surface area of ​​300-350 m². 2 / m 3 The bio-rope is a radial structure composed of elastic filaments and soft fibers, with a diameter of 70–90 mm and a specific surface area of ​​330–400 m². 2 / m 3 .

[0042] Comparative Example 1

[0043] The test water was actual wastewater generated from the desulfurization and denitrification processes, with total nitrogen (TN) ≈ 200 mg / L, including NO3. - -N accounts for more than 90%, NO2 - -N content is less than 10%, sulfate salinity is 2.7%, COD Cr The nitrogen concentration was below 30 mg / L. Three reactors, R1, R2, and R3, connected in series, were used to construct a continuous flow multi-stage anoxic-aerobic biofilm reactor for denitrification treatment of the above-mentioned experimental water. The specific process is as follows:

[0044] (1) Using salt-tolerant denitrifying sludge as the inoculum source, it was added to a mixture of combined packing material (commercially available, with a specific surface area of ​​310 m²) 2 / m 3 Composed of Φ100mm plastic rings and aldehyde-based fibers) and bio-rope (commercially available, with a specific surface area of ​​350m²). 2 / m 3 It is a radial structure made of elastic filaments and soft fiber materials (Φ80mm). It was acclimatized and cultured for one month in a pilot-scale denitrification tank using high sulfate and high nitrate nitrogen wastewater. The culture medium composition was: methanol 1000mg / L, high sulfate 3%, high nitrate nitrogen 200mg / L, potassium dihydrogen phosphate 0.5mg / L (calculated as phosphorus); the solvent was water.

[0045] (2) The mature denitrification biofilm carriers (combined packing material and bio-rope) obtained after domestication and cultivation are filled into reactors R1, R2 and R3. The filling volume of both biofilm carriers accounts for 35% of the effective volume of each reactor.

[0046] (3) Add methanol to the wastewater to be treated until the C / N ratio is 2.5, and add potassium dihydrogen phosphate, the latter being added at a rate of 0.3 mg / L.

[0047] (4) The wastewater to be treated after being supplemented with methanol and potassium dihydrogen phosphate is passed sequentially through reactors R1, R2, and R3. The effluent from R1 is used as the influent to R2, and the effluent from R2 is used as the influent to R3. Dissolved oxygen (DO) is provided by an aeration pump. In reactors R1, R2, and R3, the DO concentration of the wastewater is controlled at 0.35±0.15 mg / L (anoxic), 7.5±0.5 mg / L (aerobic), and 7.5±0.5 mg / L (aerobic), respectively. The water temperature is controlled at 25±2℃, and the hydraulic retention time (HRT) is set to 24h.

[0048] (5) After the effluent quality stabilized, the influent and effluent water quality were recorded as follows: In R1 influent, TN was 206.03±15.03mg / L and COD was 1905.69±80.87mg / L; In R1 effluent, TN was 30.32±5.54mg / L and COD was 445.67±9.43mg / L; In R2 effluent, TN was 9.16±1.07mg / L and COD was 135.54±99.54mg / L; In R3 effluent, TN was 8.35±1.03mg / L and COD was 40.92±4.86mg / L.

[0049] Comparative Example 2

[0050] After running for 15 days according to the method in Comparative Example 1, the C / N ratio of the influent R1 was changed and the operation continued. The specific steps are as follows: (1) Methanol was added to the wastewater to be treated (same as Example 1) until the C / N ratio was 2.0, and potassium dihydrogen phosphate was added. The amount of potassium dihydrogen phosphate added to the wastewater was 0.3 mg / L.

[0051] (2) The wastewater to be treated, after being supplemented with methanol and potassium dihydrogen phosphate, is sequentially passed through reactors R1, R2, and R3. The effluent from R1 is used as the influent to R2, and the effluent from R2 is used as the influent to R3. Dissolved oxygen (DO) is provided by an aeration pump. In reactors R1, R2, and R3, the DO concentration of the wastewater is controlled at 0.35±0.15 mg / L (anoxic), 7.5±0.5 mg / L (aerobic), and 7.5±0.5 mg / L (aerobic), respectively. The water temperature is controlled at 25±2℃, and the hydraulic retention time (HRT) is set to 24h.

[0052] (3) After the effluent quality stabilized, the influent and effluent water quality was recorded as follows: In R1 influent, TN was 187.98±9.20 mg / L and COD was 1570.82±43.33 mg / L; In R1 effluent, TN was 21.73±11.80 mg / L and COD was 252.33±37.71 mg / L; In R2 effluent, TN was 7.78±2.83 mg / L and COD was 77.57±32.57 mg / L; In R3 effluent, TN was 7.06±3.03 mg / L and COD was 42.53±9.69 mg / L.

[0053] Comparative Example 3

[0054] After continuing operation for 13 days using the method described in Comparative Example 2, the C / N ratio of the influent R1 was changed, and operation continued. The specific steps are as follows:

[0055] (1) Add methanol to the wastewater to be treated (same as in Example 1) until the C / N ratio is 1.5, and add potassium dihydrogen phosphate, the latter being added at a rate of 0.3 mg / L in the wastewater.

[0056] (2) The wastewater to be treated, after being supplemented with methanol and potassium dihydrogen phosphate, is sequentially passed through reactors R1, R2, and R3. The effluent from R1 is used as the influent to R2, and the effluent from R2 is used as the influent to R3. Dissolved oxygen (DO) is provided by an aeration pump. In reactors R1, R2, and R3, the DO concentration of the wastewater is controlled at 0.35±0.15 mg / L (anoxic), 7.5±0.5 mg / L (aerobic), and 7.5±0.5 mg / L (aerobic), respectively. The water temperature is controlled at 25±2℃, and the hydraulic retention time (HRT) is set to 24h.

[0057] (3) After the effluent quality stabilized, the influent and effluent water quality was recorded as follows: In R1 influent, TN was 185.34±8.93 mg / L and COD was 972.75±86.73 mg / L; In R1 effluent, TN was 10.88±1.99 mg / L and COD was 205.67±46.39 mg / L; In R2 effluent, TN was 8.12±1.64 mg / L and COD was 90.76±35.96 mg / L; In R3 effluent, TN was 8.54±2.34 mg / L and COD was 62.45±12.79 mg / L.

[0058] Comparative Example 4

[0059] After continuing to operate according to the method in Comparative Example 3 for 16 days, the HRT in each reactor was changed and operation continued. The specific steps are as follows:

[0060] (1) Add methanol to the wastewater to be treated (same as in Example 1) until the C / N ratio is 1.5, and add potassium dihydrogen phosphate, the latter being added at a rate of 0.3 mg / L in the wastewater.

[0061] (2) The wastewater to be treated, after being supplemented with methanol and potassium dihydrogen phosphate, is sequentially passed through reactors R1, R2, and R3. The effluent from R1 is used as the influent to R2, and the effluent from R2 is used as the influent to R3. Dissolved oxygen (DO) is provided by an aeration pump. In reactors R1, R2, and R3, the DO concentration of the wastewater is controlled at 0.35±0.15 mg / L (anoxic), 7.5±0.5 mg / L (aerobic), and 7.5±0.5 mg / L (aerobic), respectively. The water temperature is controlled at 25±2℃, and the hydraulic retention time (HRT) is set to 12h.

[0062] (3) After the effluent quality stabilized, the influent and effluent water quality were recorded as follows: In R1 influent, TN was 188.23±7.81 mg / L and COD was 976.45±36.58 mg / L; In R1 effluent, TN was 63.95±9.31 mg / L and COD was 358.52±66.43 mg / L; In R2 effluent, TN was 43.31±7.27 mg / L and COD was 182.88±25.83 mg / L; In R3 effluent, TN was 30.34±10.17 mg / L and COD was 130.32±13.09 mg / L.

[0063] Data analysis: The methods in Comparative Examples 1 to 3 can achieve relatively complete denitrification and have a good nitrogen removal effect, but the wastewater treatment time is too long (the total HRT in the three reactors is 72h); in Comparative Example 4, the nitrogen removal effect is not good after shortening the HRT.

[0064] Example 1

[0065] After continuing to operate according to the method in Comparative Example 4 for 33 days, the wastewater treatment conditions in R2 were changed from aerobic to anoxic and then continued to operate. The specific steps are as follows:

[0066] (1) Add methanol to the wastewater to be treated (same as in Example 1) until the C / N ratio is 1.5, and add potassium dihydrogen phosphate, the latter being added at a rate of 0.3 mg / L in the wastewater.

[0067] (2) The wastewater to be treated, after being supplemented with methanol and potassium dihydrogen phosphate, is sequentially passed through reactors R1, R2, and R3. The effluent from R1 is used as the influent to R2, and the effluent from R2 is used as the influent to R3. Dissolved oxygen (DO) is provided by an aeration pump. In reactors R1, R2, and R3, the DO concentration of the wastewater is controlled at 0.35±0.15 mg / L (anoxic), 0.35±0.15 mg / L (anoxic), and 7.5±0.5 mg / L (aerobic), respectively. The water temperature is controlled at 25±2℃, and the hydraulic retention time (HRT) is set to 12h.

[0068] (3) After the effluent quality stabilized, the influent and effluent water quality were recorded as follows: In R1 influent, TN was 191.54±7.38 mg / L and COD was 1031.62±70.85 mg / L; In R1 effluent, TN was 43.23±5.44 mg / L and COD was 525.67±68.80 mg / L; In R2 effluent, TN was 25.35±8.24 mg / L and COD was 306.51±17.80 mg / L; In R3 effluent, TN was 12.97±7.99 mg / L and COD was 251.92±33.06 mg / L.

[0069] Data analysis: Example 1 achieved better nitrogen removal effect, which was significantly better than Comparative Example 4. This shows that compared with the three-stage treatment process of anoxic-aerobic-aerobic, the anoxic-anoxic-aerobic method can achieve better nitrogen removal effect.

[0070] Example 2

[0071] After continuing operation for 14 days according to the method in Example 1, the C / N ratio of the R1 influent was changed and operation continued. The specific steps are as follows:

[0072] (1) Add methanol to the wastewater to be treated (same as in Example 1) until the C / N ratio is 1.25, and add potassium dihydrogen phosphate, the latter being added at a rate of 0.3 mg / L in the wastewater.

[0073] (2) The wastewater to be treated, after being supplemented with methanol and potassium dihydrogen phosphate, is sequentially passed through reactors R1, R2, and R3. The effluent from R1 is used as the influent to R2, and the effluent from R2 is used as the influent to R3. Dissolved oxygen (DO) is provided by an aeration pump. In reactors R1, R2, and R3, the DO concentration of the wastewater is controlled at 0.35±0.15 mg / L (anoxic), 0.35±0.15 mg / L (anoxic), and 7.5±0.5 mg / L (aerobic), respectively. The water temperature is controlled at 25±2℃, and the hydraulic retention time (HRT) is set to 12h.

[0074] (3) After the effluent quality stabilized, the influent and effluent water quality was recorded as follows: In R1 influent, TN was 196.79±5.19 mg / L and COD was 808.17±46.23 mg / L; In R1 effluent, TN was 33.85±11.20 mg / L and COD was 206.22±61.19 mg / L; In R2 effluent, TN was 24.73±12.15 mg / L and COD was 191.27±26.33 mg / L; In R3 effluent, TN was 22.53±10.35 mg / L and COD was 147.14±10.67 mg / L.

[0075] Data analysis: Compared with Example 1, the denitrification effect of Example 2 decreased, but the COD in the effluent of R3 decreased, indicating that reducing the amount of external carbon source added to a certain extent (reducing the C / N ratio of the influent of R1) can reduce the amount of organic matter residue in the effluent, but it will have an adverse effect on the denitrification effect.

[0076] Unless otherwise specified, the raw materials and equipment used in this invention are all commonly used in the field; unless otherwise specified, the methods used in this invention are all conventional methods in the field.

[0077] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, alterations, and equivalent transformations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for denitrification treatment of high-sulfate and high-nitrate nitrogen wastewater, characterized in that, Includes the following steps: (1) Biofilm carriers are filled into the anoxic zone I, anoxic zone II and aerobic zone. Salt-tolerant hypoxic denitrifying bacteria are attached to the biofilm carriers in the anoxic zone I and anoxic zone II, and salt-tolerant aerobic denitrifying bacteria are attached to the biofilm carriers in the aerobic zone. (2) Adjust the carbon-nitrogen ratio of the wastewater to be treated to 1.25~1.5, and then introduce it into the anoxic zone I for primary anoxic biological treatment; (3) The effluent from anoxic zone I is introduced into anoxic zone II for secondary biological anoxic treatment; (4) The effluent from the anoxic zone II is introduced into the aerobic zone for aerobic biological treatment; The dissolved oxygen concentration of wastewater in anoxic zone I and anoxic zone II is controlled at 0.2~0.5 mg / L, and the temperature is controlled at 23~27℃; the dissolved oxygen concentration of wastewater in aerobic zone is controlled at 7.0~8.0 mg / L, and the temperature is controlled at 23~27℃.

2. The denitrification treatment method as described in claim 1, characterized in that, In step (2), when the carbon-nitrogen ratio of the wastewater to be treated is less than 1.25~1.5, methanol is added to adjust the carbon-nitrogen ratio to 1.25~1.

5.

3. The denitrification treatment method as described in claim 1, characterized in that, In step (2), the hydraulic residence time in the anoxic zone I is 12-15 h.

4. The denitrification treatment method as described in claim 1, characterized in that, In step (3), the hydraulic residence time in the anoxic zone II is 12-15 h.

5. The denitrification treatment method as described in claim 1, characterized in that, In step (4), the hydraulic residence time in the aerobic zone is 12-24 h.

6. The denitrification treatment method as described in claim 1, characterized in that, In step (2), a phosphorus source is added to the wastewater before it is introduced into the anoxic zone I.

7. The denitrification treatment method as described in claim 6, characterized in that, The amount of phosphorus source added is 0.3~0.6 mg / L.

8. The denitrification treatment method as described in claim 1, characterized in that, In step (1), the filling volume of the biofilm carrier in the hypoxic zone I, hypoxic zone II and aerobic zone is 60-70% of the effective volume.

9. The denitrification treatment method as described in claim 1 or 8, characterized in that, In step (1), the biofilm carrier is composed of a combined packing material and bio-ropes, and the specific surface area of ​​the combined packing material is 300~350 m². 2 / m 3 The specific surface area of ​​the bio-rope is 330~400 m². 2 / m 3 .