Method for realizing municipal sewage denitrification by combining pre-oxidation with nano zero-valent iron loaded activated carbon carrier

Abstract

The invention discloses a method for realizing municipal sewage denitrification by combining pre-oxidation with a nano zero-valent iron loaded activated carbon carrier, and aims to solve the problems of slow growth speed of iron ammonia oxidation microorganisms, poor denitrification effect and the like in an iron ammonia oxidation process. The water treatment method comprises the following steps: 1, adding ferrate into municipal sewage to carry out pre-oxidation treatment, and adding polymeric ferric sulfide to carry out enhanced coagulation treatment; 2, inoculating mixed sludge into the SBR bioreactor, wherein the mixed sludge is composed of anaerobic ammonia oxidation granular sludge and municipal sludge; 3, introducing inert gas into the SBR reactor; and 4, introducing the pre-oxidized and coagulated sewage supernatant as inlet water into an SBR (Sequencing Batch Reactor) inoculated with sludge, and regularly adding carbon-loaded nano zero-valent iron into the SBR to complete denitrification of the municipal sewage. According to the invention, ferrate is added into municipal sewage for pre-oxidation through the front end, so that partial removal of organic matters and phosphorus is realized, and nitrogen removal of sewage is realized in combination with an activated carbon carrier loaded with nano zero-valent iron at the rear end.

Description

Technical Field

[0001] The present invention belongs to the technical field of municipal sewage treatment, and specifically relates to a method for strengthening iron-ammonia oxidation denitrification and removing other pollutants by combining advanced oxidation technology with carbon-supported nano-zero-valent iron. Background Art

[0002] Reducing the energy consumption of sewage treatment and achieving green and sustainable treatment methods are the ultimate goals of sewage treatment plants. Through ferrate pre-oxidation and front-end coagulation, organic matter and phosphorus in sewage are captured, and resources are recovered through subsequent treatment methods. The added iron-based oxidants and coagulants can be used as electron acceptors in the subsequent denitrification process to achieve secondary utilization.

[0003] Feammox technology is a technology that uses Fe 3+ NH4 + A new type of autotrophic biological denitrification process that oxidizes to nitrogen gas has the characteristics of less sludge production, simple process and reduced treatment energy consumption compared with traditional nitrification-denitrification process and anaerobic ammonium oxidation process. However, it has the characteristics of slow growth rate of iron-ammonia oxidizing microorganisms, long era time and strict requirements for anaerobic environment, which leads to difficulties in enriching iron-ammonia oxidizing microorganisms, slow reactor startup and unstable movement, affecting the application of this technology in the field of sewage treatment.

[0004] Nano-zero-valent iron has a large specific surface area, strong reducing properties, and strong reactivity. It can quickly consume dissolved oxygen in water, reduce the redox potential, and ensure an anaerobic environment in the reactor. Biochar, as an electron shuttle, can accelerate the electrons in NH4 + and Fe 3+ On the other hand, biochar, as a carrier, can gather iron-ammonia oxidizing microorganisms to form micro-communities, ensuring stable and reliable removal effects. Summary of the invention

[0005] The purpose of the present invention is to solve the problems of slow growth rate of iron-ammonia oxidation microorganisms in the iron-ammonia oxidation process, strict requirements for anaerobic environment, poor denitrification effect, etc., and to provide a method for denitrification of municipal sewage by pre-oxidation combined with activated carbon carrier loaded with nano zero-valent iron. Front-end oxidation and coagulation provide electron acceptors for subsequent iron-ammonia oxidation treatment, and at the same time, carbon-supported nano zero-valent iron is added to provide microbial growth carriers and electron shuttles for iron-ammonia oxidation.

[0006] The method for denitrification of municipal sewage by pre-oxidation combined with nano-zero-valent iron-loaded activated carbon carrier is implemented according to the following steps:

[0007] Step 1: adding ferrate to municipal sewage for pre-oxidation treatment, and then adding polyferric sulfide for enhanced coagulation treatment, and obtaining pre-oxidation and coagulation treated sewage after static sedimentation;

[0008] Step 2, inoculating mixed sludge into the SBR bioreactor, the mixed sludge consisting of anaerobic ammonium oxidation granular sludge and municipal sludge, to obtain an SBR reactor inoculated with sludge;

[0009] Step 3: introducing inert gas into the SBR reactor inoculated with sludge to create an anaerobic environment;

[0010] Step 4: The sewage supernatant after pre-oxidation and coagulation treatment is used as the influent, and is passed into the SBR reactor inoculated with sludge. Carbon-supported nano-zero-valent iron is regularly added to the SBR reactor, and the temperature in the reactor is controlled to be 32-37° C., and the hydraulic retention time is 5-10 hours, so as to complete the denitrification of municipal sewage;

[0011] The preparation method of carbon-supported nano-zero-valent iron in step 4 is as follows:

[0012] a. Washing and drying the biochar particles, and sieving to obtain biochar particles with a particle size of 0.15-0.5 mm;

[0013] b. Dissolve FeSO4●7H2O in an ethanol solution, add the biochar particles in step 1, and obtain a FeSO4-biochar loaded reaction solution after ultrasonic dispersion treatment;

[0014] c. Under an inert atmosphere, add NaBH4 solution dropwise to the FeSO4-biochar-loaded reaction solution obtained in step b, stir and react for 40-80 min, and wash and dry the solid phase to obtain carbon-supported nano-zero-valent iron.

[0015] The method for denitrification of municipal sewage by pre-oxidation combined with nanometer zero-valent iron-loaded activated carbon carrier of the present invention includes the following beneficial effects:

[0016] 1. The present invention utilizes front-end pre-oxidation and coagulation to remove some organic pollutants and phosphorus-containing pollutants in sewage, and adopts an innovative method to recover C and P elements in sludge.

[0017] 2. A small amount of iron species in the supernatant after pre-oxidation coagulation and sedimentation enters the reactor to replenish the consumption of iron species in the SBR reactor, thus realizing a virtuous cycle of iron-ammonia oxidation.

[0018] 3. The present invention uses carbon-supported nano-zero-valent iron to strengthen iron-ammonia oxidation denitrification, which can shorten the start-up time of the iron-ammonia oxidation process and promote the immobilization of iron-ammonia oxidation sludge. The addition of nano-zero-valent iron helps to eliminate dissolved oxygen and maintain the anaerobic environment in the bioreactor; at the same time, the iron ions released by nano-iron oxide can promote nitrate reduction as a biologically available electron donor, further enhancing the denitrification performance of the reactor.

[0019] 4. In the process of preparing carbon-supported nano zero-valent iron of the present invention, FeSO4·7H2O is dissolved in 75% ethanol solution, biochar is added for dispersion and mixing, and finally NaBH4 solution is added dropwise for stirring and reaction to obtain the required carbon-supported nano zero-valent iron. The carbon-supported nano zero-valent iron prepared by the present invention has good uniformity and high bonding strength, and has significant effects on enriching iron-ammonia oxidizing microorganisms and improving the denitrification performance of the reactor. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The schematic diagram of the structure of the SBR bioreactor in the embodiment;

[0021] Figure 2 This is a test diagram of ammonia nitrogen and total nitrogen removal rates of the R1 reactor in the embodiment;

[0022] Figure 3 This is a test diagram of COD concentration change in the effluent of the R1 reactor in the embodiment;

[0023] Figure 4 This is a test diagram of the concentration changes of nitrite nitrogen and nitrate nitrogen in the effluent of the R1 reactor in the embodiment;

[0024] Figure 5 This is a test diagram of ammonia nitrogen and total nitrogen removal rates of the R2 reactor in the embodiment;

[0025] Figure 6 This is a test diagram of COD concentration change in the effluent of the R2 reactor in the embodiment;

[0026] Figure 7 This is a test diagram of the change in the concentration of nitrite nitrogen and nitrate nitrogen in the effluent of the R2 reactor in the embodiment;

[0027] Figure 8 This is a test diagram of ammonia nitrogen and total nitrogen removal rates of the R3 reactor in the embodiment;

[0028] Fig. 9 This is a test diagram of COD concentration change in the effluent of the R3 reactor in the embodiment;

[0029] Fig.10 This is a test chart of the changes in the concentrations of nitrite nitrogen and nitrate nitrogen in the effluent of the R3 reactor in the embodiment. DETAILED DESCRIPTION

[0030] Specific implementation method 1: In this implementation method, the method for denitrification of municipal sewage by pre-oxidation combined with nano-zero-valent iron-loaded activated carbon carrier is implemented according to the following steps:

[0031] Step 1: adding ferrate to municipal sewage for pre-oxidation treatment, and then adding polyferric sulfide for enhanced coagulation treatment, and obtaining pre-oxidation and coagulation treated sewage after static sedimentation;

[0032] Step 2, inoculating mixed sludge into the SBR bioreactor, the mixed sludge consisting of anaerobic ammonium oxidation granular sludge and municipal sludge, to obtain an SBR reactor inoculated with sludge;

[0033] Step 3: introducing inert gas into the SBR reactor inoculated with sludge to create an anaerobic environment;

[0034] Step 4: The sewage supernatant after pre-oxidation and coagulation treatment is used as the influent, and is passed into the SBR reactor inoculated with sludge. Carbon-supported nano-zero-valent iron is regularly added to the SBR reactor, and the temperature in the reactor is controlled to be 32-37° C., and the hydraulic retention time is 5-10 hours, so as to complete the denitrification of municipal sewage;

[0035] The preparation method of carbon-supported nano-zero-valent iron in step 4 is as follows:

[0036] a. Washing and drying the biochar particles, and sieving to obtain biochar particles with a particle size of 0.15-0.5 mm;

[0037] b. Dissolve FeSO4·7H2O in an ethanol solution, add the biochar particles in step 1, and obtain a FeSO4-biochar loaded reaction solution after ultrasonic dispersion treatment;

[0038] c. Under an inert atmosphere, add NaBH4 solution dropwise to the FeSO4-biochar-loaded reaction solution obtained in step b, stir and react for 40-80 min, and wash and dry the solid phase to obtain carbon-supported nano-zero-valent iron.

[0039] During the stable operation of the reactor in step 4 of this embodiment, carbon-supported nano-zero-valent iron is added at intervals of 3 days, and the addition amount is controlled to be 5 g / L based on the volume of sewage.

[0040] This embodiment discloses a method for denitrifying municipal sewage by pre-oxidation combined with activated carbon carrier loaded with nano zero-valent iron, which achieves partial removal of organic matter and phosphorus by adding ferrate to municipal sewage for pre-oxidation at the front end, and realizes denitrification of sewage by combining with activated carbon carrier loaded with nano zero-valent iron at the back end. The activated carbon carrier loaded with nano zero-valent iron maintains the anaerobic environment of the reactor and promotes electron transfer. At the same time, the granular activated carbon acts as a biological carrier to better enrich the denitrification microbial population and achieve the removal of total nitrogen, ammonia nitrogen, nitrate nitrogen and nitrite nitrogen in sewage. The municipal sewage denitrification method has the advantages of simple structure, fast start-up time and stable removal effect. The municipal sewage denitrification method can adjust the enrichment degree of functional bacteria by adjusting pH, hydraulic retention time, inoculation ratio, carrier dosage and zero-valent iron loading.

[0041] Specific implementation method 2: The difference between this implementation method and specific implementation method 1 is that in step 1, the dosage of ferrate is controlled to be 50-100 mg / L, and the dosage of polyferric sulfate is controlled to be 30-40 mg / L.

[0042] Specific implementation method three: This implementation method is different from specific implementation methods one or two in that the ferrate described in step one is potassium ferrate.

[0043] Specific implementation method 4: This implementation method is different from specific implementation methods 1 to 3 in that the settling time in step 1 is 30-60 minutes.

[0044] Specific implementation mode 5: This implementation mode is different from specific implementation modes 1 to 4 in that the wall of the SBR bioreactor in step 2 is a hollow cavity wall, and water bath hot water circulates in the hollow cavity wall.

[0045] Specific implementation method six: This implementation method is different from specific implementation methods one to five in that the mixed sludge in step two is composed of anaerobic ammonium oxidation granular sludge and municipal sludge in a mass ratio of 1:1, and the MLSS of the anaerobic ammonium oxidation granular sludge is controlled to be 2000-2200 mg / L, and the MLSS of the municipal sludge is 2000-2200 mg / L.

[0046] In this embodiment, the municipal sludge comes from fresh sludge collected from a biochemical pool of a water plant in Harbin, and the anaerobic ammonium oxidation granular sludge is commercially available anaerobic ammonium oxidation bacteria Anammox granular sludge.

[0047] Specific implementation method 7: This implementation method is different from any one of specific implementation methods 1 to 6 in that the inert gas described in step 3 is nitrogen, argon or carbon dioxide.

[0048] Specific embodiment eight: This embodiment differs from any one of specific embodiments one to seven in that the amount of carbon-supported nano zero-valent iron added to the SBR reactor in step four is based on the volume of sewage, and the amount is controlled to be 4-8 g / L.

[0049] Specific embodiment nine: The difference between this embodiment and any one of specific embodiments one to eight is that in the preparation method of carbon-supported nano zero-valent iron, in step b, FeSO4·7H2O is dissolved in an ethanol solution, and the mass ratio of FeSO4·7H2O to biochar is controlled to be 1:(25-40).

[0050] Specific embodiment ten: The difference between this embodiment and any one of specific embodiments one to nine is that in the preparation method of carbon-supported nano zero-valent iron, the concentration of the NaBH4 solution in step c is 1-1.2 mol / L, and the mass ratio of NaBH4 to biochar is 1:(4-6).

[0051] Example 1: The method for denitrification of municipal sewage by pre-oxidation combined with nano-zero-valent iron-loaded activated carbon carrier is implemented according to the following steps:

[0052] Step 1: adding potassium ferrate to municipal sewage for pre-oxidation treatment for 10 minutes, the dosage of potassium ferrate is 20.0 mg / L, and then adding polyferric sulfide for enhanced coagulation treatment for 15 minutes, the dosage of polyferric sulfide is 20.0 mg / L, and after settling for 40 minutes, the pre-oxidation and coagulation treatment sewage is obtained;

[0053] Step 2, inoculating mixed sludge into the SBR bioreactor, the mixed sludge consisting of anaerobic ammonium oxidation granular sludge and municipal sludge in a mass ratio of 1:1, the MLSS of the anaerobic ammonium oxidation granular sludge is 2200 mg / L, and the MLSS of the municipal sludge is 2200 mg / L, to obtain an SBR reactor inoculated with sludge;

[0054] Step 3: introducing inert gas into the SBR reactor inoculated with sludge for 20 minutes to create an anaerobic environment;

[0055] Step 4: The supernatant of the sewage after pre-oxidation and coagulation treatment is used as the influent, and is passed into the SBR reactor inoculated with sludge, and carbon-supported nano-zero-valent iron is added to the SBR reactor. The amount of carbon-supported nano-zero-valent iron added is controlled to be 5 g / L based on the volume of sewage, and the temperature in the reactor is controlled to be 35±1°C, the stirring speed is 120 r / min, the pH is 7.5±0.1, and the hydraulic retention time is 6 h to complete the denitrification of municipal sewage;

[0056] Step 5: Use a peristaltic pump to control the water inlet and outlet of the reactor, and measure the concentration changes of the effluent nitrogen index (total nitrogen, ammonia nitrogen, nitrate nitrogen and nitrite nitrogen) and the organic matter index (COD) every day during the operation;

[0057] The preparation method of carbon-supported nano-zero-valent iron in step 4 is as follows:

[0058] a. Wash the biochar particles, dry them at 80°C for 36 hours, and sieve them to obtain biochar particles with a particle size of 0.15-0.5 mm;

[0059] b. Dissolve FeSO4·7H2O in 75% ethanol solution, add the biochar particles in step 1, control the mass ratio of FeSO4 to biochar to be 1:30, and obtain FeSO4-biochar loaded reaction solution after ultrasonic dispersion treatment for 30 minutes;

[0060] c. Under N2 atmosphere, NaBH4 solution was added dropwise to the FeSO4-biochar-loaded reaction solution. The mass ratio of the added NaBH4 to the biochar particles was 1:5. The stirring speed was controlled at 300 rpm. The stirring reaction was continued for 60 min. The solid phase was washed and dried to obtain carbon-supported nano-zero-valent iron.

[0061] The structural schematic diagram of the SBR reactor in this embodiment is as follows Figure 1 As shown, the wall of the reactor 1 is a hollow cavity wall 2, and hot water for a water bath circulates in the hollow cavity wall. A thermometer 3 and a DO detector are arranged on the top cover of the reactor 1, and an exhaust hole 4 is also opened on the top cover.

[0062] The start-up conditions of this embodiment are as follows: an SBR reactor with an effective volume of 2L is used as the reactor for iron-ammonia oxidation, the inoculated sludge is the cultured anaerobic ammonium oxidation granular sludge and the activated sludge of the municipal sewage plant, the influent is the supernatant after ferrate pre-oxidation and polyferric sulfate coagulation precipitation, and the influent NH4 + The concentration is about 40 mg / L, nitrate nitrogen is about 2 mg / L, nitrite nitrogen is almost non-existent, COD is about 180-200 mg / L, hydraulic retention time HRT is 6h, and the biochar carrier occupies 5-10% of the effective volume of the SBR reactor.

[0063] Comparative Example 1: The difference between this embodiment and Example 1 is that in step four, biochar without nano zero-valent iron loading is added, and other conditions are the same as those in the embodiment. The biochar addition amount is 5 g / L, the temperature in the reactor is controlled to be 35±1°C, the stirring speed is 120 r / min, the pH is 7.5±0.1, and the hydraulic retention time is 6 h.

[0064] Comparative Example 2: This embodiment combines pre-oxidation with nano zero-valent iron and activated carbon carrier to achieve municipal sewage denitrification method, which specifically includes the following steps:

[0065] S1. Ferrate and polyferric sulfide are added to municipal sewage in sequence, and organic matter and phosphorus in municipal sewage are removed by pre-oxidation and enhanced coagulation to reduce sewage turbidity, and the sewage is introduced into the SBR bioreactor after settling for a period of time;

[0066] S2. In the SBR reactor, anaerobic ammonium oxidation granular sludge and municipal sludge are inoculated so that the mixed sludge occupies 1 / 3-1 / 4 of the reactor volume;

[0067] S3, passing an inert gas into the SBR reactor in step S2 for 20 minutes to remove dissolved oxygen;

[0068] S4, using the municipal sewage treated by S1 as the influent, controlling the temperature in the reactor to 35±1°C, the stirring speed to 120r / min, the pH to 7.5±0.1, and the hydraulic retention time to 6h. After the reactor runs stably, adding commercial nano zero-valent iron to the reactor and keeping the reactor running stably, adding biochar particles to the reactor daily, based on the volume of wastewater, without adding any other substances, and keeping the reactor running stably;

[0069] S5. Use a peristaltic pump to control the water inlet and outlet of the reactor, and measure the changes in the concentration of effluent nitrogen indicators (total nitrogen, ammonia nitrogen, nitrate nitrogen and nitrite nitrogen) and organic matter indicators (COD) every day during operation.

[0070] Example 1 is recorded as R1 (carbon-supported nano-zero-valent iron group), Comparative Example 1 is recorded as R2 (biochar particle group), and Comparative Example 2 is recorded as R3 (nano-zero-valent iron group). The iron-ammonia oxidation denitrification performance of Example, Comparative Example 1 and Comparative Example 2 is compared, and the following results are obtained:

[0071] In the first stage (0-20d), the three SBR bioreactors of Example, Comparative Example 1 and Comparative Example 2 all had good denitrification effects, among which all three reactors showed a certain denitrification capacity, and COD also had a certain removal effect. The ammonia nitrogen removal rates of R1, R2 and R3 reactors were 97.4%, 82.4% and 82.2% at 20 days, the total nitrogen removal rates were 88.6%, 63.8% and 63.2%, and the COD removal rates were 58.4%, 43.2% and 32.2%.

[0072] In the second stage (21-40d), the effluent quality of R2 and R3 reactors deteriorated rapidly, while R1 showed excellent and stable performance, with the denitrification efficiency maintained at 80%, significantly higher than 40% and 30% of R2 and R3. The ammonia nitrogen removal rates of R1, R2 and R3 reactors at 20 days were 95.0%, 77.2% and 68.0%, the total nitrogen removal rates were 86.9%, 37.6% and 26.7%, and the COD removal rates were 55.4%, 44.6% and 36.1%.

[0073] In the first stage, the three reactors R1, R2 and R3 rely on municipal sludge microorganisms to remove COD and ammonia nitrogen oxidation, and anaerobic ammonia oxidizing microorganisms to achieve ammonia nitrogen removal. In the second stage, as the reactor is running, the dissolved oxygen in the reactor gradually increases, which has an inhibitory effect on anaerobic iron ammonia oxidizing microorganisms. The addition of carbon-supported nano zero-valent iron is beneficial to the creation of an anaerobic environment on the one hand, and biochar can play the role of electron shuttle and carrier, which is beneficial to the enrichment of microorganisms on the surface of biochar and electron transfer, and realizes the oxidation and removal of ammonia nitrogen. Biochar alone and nano zero-valent iron alone are insufficient in mass transfer and anaerobic atmosphere creation, and the denitrification capacity of the reactor is limited.

[0074] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make modifications to the present embodiment without any creative contribution as needed, but such modifications are protected by the patent law as long as they are within the scope of the claims of the present application.

Claims

1. A method for denitrification of municipal sewage by pre-oxidation combined with nano-zero-valent iron-loaded activated carbon carrier, characterized in that The method for denitrification of municipal sewage by pre-oxidation combined with nano-zero-valent iron-loaded activated carbon carrier is implemented according to the following steps: Step 1: adding ferrate to municipal sewage for pre-oxidation treatment, and then adding polyferric sulfide for enhanced coagulation treatment, and obtaining pre-oxidized and coagulated sewage after static sedimentation; Step 2, inoculating mixed sludge into the SBR bioreactor, the mixed sludge consisting of anaerobic ammonium oxidation granular sludge and municipal sludge, to obtain an SBR reactor inoculated with sludge; Step 3: introducing inert gas into the SBR reactor inoculated with sludge to create an anaerobic environment; Step 4: The sewage supernatant after pre-oxidation and coagulation treatment is used as the influent, and is passed into the SBR reactor inoculated with sludge. Carbon-supported nano-zero-valent iron is regularly added to the SBR reactor, and the temperature in the reactor is controlled to be 32-37° C., and the hydraulic retention time is 5-10 hours, so as to complete the denitrification of municipal sewage; The preparation method of carbon-supported nano-zero-valent iron in step 4 is as follows: a. Washing and drying the biochar particles, and sieving to obtain biochar particles with a particle size of 0.15-0.5 mm; b. Dissolve FeSO4·7H2O in an ethanol solution, add the biochar particles in step 1, and obtain a FeSO4-biochar loaded reaction solution after ultrasonic dispersion treatment; c. Under an inert atmosphere, add NaBH4 solution dropwise to the FeSO4-biochar-loaded reaction solution obtained in step b, stir and react for 40-80 min, and wash and dry the solid phase to obtain carbon-supported nano-zero-valent iron.

2. The method for denitrification of municipal sewage by pre-oxidation combined with nano-zero-valent iron-loaded activated carbon carrier according to claim 1 is characterized in that In step 1, the dosage of ferrate is controlled to be 50-100 mg / L, and the dosage of polyferric sulfate is controlled to be 30-40 mg / L.

3. The method for denitrification of municipal sewage by pre-oxidation combined with nano-zero-valent iron-loaded activated carbon carrier according to claim 1, characterized in that The ferrate described in step 1 is potassium ferrate.

4. The method for denitrification of municipal sewage by pre-oxidation combined with nano-zero-valent iron-loaded activated carbon carrier according to claim 1, characterized in that The settling time in step 1 is 30-60 minutes.

5. The method for denitrification of municipal sewage by pre-oxidation combined with nano-zero-valent iron-loaded activated carbon carrier according to claim 1, characterized in that In step 2, the wall of the SBR bioreactor is a hollow cavity wall, and hot water from a water bath circulates in the hollow cavity wall.

6. The method for denitrification of municipal sewage by pre-oxidation combined with nano-zero-valent iron-loaded activated carbon carrier according to claim 1, characterized in that In step 2, the mixed sludge consists of anaerobic ammonium oxidation granular sludge and municipal sludge in a mass ratio of 1:1, and the MLSS of the anaerobic ammonium oxidation granular sludge is controlled to be 2000-2200 mg / L, and the MLSS of the municipal sludge is controlled to be 2000-2200 mg / L.

7. The method for denitrification of municipal sewage by pre-oxidation combined with nano-zero-valent iron-loaded activated carbon carrier according to claim 1, characterized in that The inert gas described in step 3 is nitrogen, argon or carbon dioxide.

8. The method for denitrification of municipal sewage by pre-oxidation combined with nano-zero-valent iron-loaded activated carbon carrier according to claim 1, characterized in that In step 4, the amount of carbon-supported nano-zero-valent iron added to the SBR reactor is calculated based on the volume of sewage, and the amount is controlled to be 4-8 g / L.

9. The method for denitrification of municipal sewage by pre-oxidation combined with nano-zero-valent iron-loaded activated carbon carrier according to claim 1, characterized in that In the preparation method of carbon-supported nano-zero-valent iron, in step b, FeSO4·7H2O is dissolved in an ethanol solution, and the mass ratio of FeSO4·7H2O to biochar is controlled to be 1:(25-40).

10. The method for denitrification of municipal sewage by pre-oxidation combined with nano-zero-valent iron-loaded activated carbon carrier according to claim 1, characterized in that In the preparation method of carbon-supported nano-zero-valent iron, the concentration of the NaBH4 solution in step c is 1-1.2 mol / L, and the mass ratio of NaBH4 to biochar is 1:(4-6).

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