Town sewage treatment process based on denitrification nitrogen removal

Abstract

The invention relates to the technical field of sewage treatment, in particular to an urban sewage treatment process based on nitrogen removal by denitrification. A town sewage treatment process based on nitrogen removal by denitrification comprises the following steps: sewage pretreatment, nitration reaction and nitrogen removal by denitrification reaction: preparing fixed carrier microspheres which have good mechanical strength, adsorption performance and mass transfer performance as a carrier; according to the invention, the immobilized carrier microspheres are used as a carrier, transmission of nutrients and metabolites and growth and reproduction of denitrifying bacteria are facilitated, the denitrifying bacteria attached and fixed in the immobilized carrier microspheres can utilize nitrate ions, COD and a carbon source adsorbed in the immobilized carrier microspheres to promote the denitrifying bacteria to carry out a denitrification nitrogen removal reaction, COD in sewage is efficiently removed, and the denitrification efficiency is improved. Meanwhile, the nitrogen removal efficiency of denitrification is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of sewage treatment, and more specifically, to a process for treating urban sewage based on denitrification and denitrification. Background Art

[0002] Nitrogen pollution is an important cause of water pollution. Urban sewage contains a certain amount of nitrogen. Therefore, denitrification is almost an essential step in the treatment of urban sewage. The commonly used biological denitrification process consists of nitrification and denitrification reactions.

[0003] Although the denitrification and denitrification processes for treating wastewater in the prior art have achieved certain results, there are still some deficiencies and shortcomings. For example, the carrier material used to load the denitrifying bacteria has poor structural stability and low mass transfer efficiency, which results in the inability of the carrier material to maintain its shape and structural integrity in a complex hydraulic environment, causing damage and loss of the carrier, which in turn results in the inability of the denitrifying bacteria to be stably fixed on the carrier material, making it easy for the denitrifying bacteria to be lost with the water flow and difficult to recycle. In addition, it affects the transmission of nutrients and metabolites on the carrier material and the growth and reproduction of the denitrifying bacteria, resulting in a slow proliferation rate of the denitrifying bacteria and affecting the efficiency of the denitrification and denitrification reaction. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention provides a process for treating urban sewage based on denitrification.

[0005] A process for treating urban sewage based on denitrification and denitrification comprises the following steps:

[0006] Step S1: sewage pretreatment: the sewage is passed through a screen tank to block floating objects and larger solid particles in the sewage;

[0007] Step S2: nitrification reaction: aeration treatment and nitrification reaction are performed on the pretreated sewage, and the sewage after nitrification treatment is passed into an intermediate sedimentation tank to precipitate sludge to obtain sewage after nitrification treatment;

[0008] Step S3: denitrification and denitrification reaction: introducing the wastewater that has completed the nitrification treatment into the denitrification treatment pool, adding a carbon source and using fixed carrier microspheres to carry out denitrification and denitrification reaction on the wastewater in the denitrification treatment pool. After the denitrification treatment is completed, the effluent water quality is tested;

[0009] The fixed carrier microspheres are prepared from modified polyvinyl alcohol, carboxymethyl cellulose, doped coal gangue and cross-linking agent as raw materials;

[0010] Doped coal gangue is obtained by combining coal gangue, potassium oxide and magnesium oxide as raw materials through hot alkali reaction to combine potassium element of potassium oxide and magnesium element of magnesium oxide with coal gangue;

[0011] The modified polyvinyl alcohol is prepared by taking radiation-treated polyvinyl alcohol, glycidyl methacrylate, nano-ferric oxide and deionized water as raw materials.

[0012] Furthermore, the preparation of doped coal gangue specifically includes the following steps:

[0013] The coal gangue, potassium oxide and magnesium oxide are mixed and stirred in a mass ratio of (10-15): (0.1-1): (0.1-1) and ball-milled to obtain a mixed material, the mixed material is poured into a sodium hydroxide solution with a concentration of 2 mol / L, microwave-treated at 150-180° C. for 30-40 min, and then stirred and aged at 28-36° C. for 4-6 h to obtain a mineral liquid mixture;

[0014] The ore-liquid mixture is reacted at a high temperature of 180-220° C. for 3-5 hours to obtain doped coal gangue.

[0015] Furthermore, the preparation of modified polyvinyl alcohol specifically comprises the following steps:

[0016] The nano-iron trioxide and deionized water are stirred and mixed in a mass ratio of (0.1-0.3):1, and then ultrasonically treated for 3-5 minutes to obtain a nano-iron trioxide dispersion liquid, glycidyl methacrylate and Tween 20 are stirred and mixed in a mass ratio of (10-40):(2-5) to obtain a mixture, and the nano-iron tetroxide dispersion liquid and the mixture are mixed in a mass ratio of (0.2-1):1 to obtain a reaction solution, which is stored under a nitrogen atmosphere for later use;

[0017] The polyvinyl alcohol is placed in a vacuum sealed bag and irradiated at 6 to 15°C for 5 to 10 minutes;

[0018] After the irradiation is completed, the polyvinyl alcohol is immediately taken out from the vacuum sealed bag and quickly added to the reaction solution, and the reaction is stirred at 42 to 48° C. for 2 to 4 hours. After suction filtration, washing and drying, the modified polyvinyl alcohol is obtained.

[0019] Furthermore, the dose rate of the irradiation treatment is 3 to 8 kGy / Pass, and the total dose is 10 to 30 kGy.

[0020] Furthermore, the preparation of the fixed carrier microspheres specifically includes the following steps:

[0021] 12 to 24 parts by weight of modified polyvinyl alcohol are added to 80 to 150 parts by weight of deionized water, and stirred at 92 to 98° C. for 10 to 15 minutes to obtain a modified polyvinyl alcohol solution. In a nitrogen atmosphere, 1 to 5 parts by weight of carboxymethyl cellulose and 0.6 to 5 parts by weight of doped coal gangue are sequentially added to the modified polyvinyl alcohol solution, and stirred for 30 to 60 minutes to obtain a composite gel solution.

[0022] The composite gel solution is injected into the mold, and the mold after injection is placed in a refrigerator at -20°C for 8 to 12 hours, and the mold is demolded after molding to obtain gel microspheres, and the gel microspheres are added to the crosslinking agent and stirred at 22 to 30°C for 10 to 20 minutes;

[0023] Subsequently, the cross-linked gel microspheres were taken out and placed in a refrigerator at 3 to 6° C. for refrigeration and solidification for 12 to 24 hours, and then washed with deionized water for 2 to 3 times to obtain fixed carrier microspheres.

[0024] Furthermore, the cross-linking agent is a saturated boric acid solution of calcium chloride with a mass fraction of 5%.

[0025] Furthermore, the mold is a spherical mold with a diameter of 3 to 5 mm.

[0026] Furthermore, the nitrification reaction temperature is 18-30°C, the dissolved oxygen is ≥2 mg / L, and the pH is 7-8.

[0027] Furthermore, the denitrification reaction temperature is 20-35°C, the dissolved oxygen is <5 mg / L, and the pH is 7-7.5.

[0028] Furthermore, the carbon source is at least one of methanol, sodium acetate or glucose.

[0029] The present invention has the following advantages:

[0030] 1. In the present invention, coal gangue, potassium oxide and magnesium oxide are used as raw materials, and the potassium component of potassium oxide and the magnesium component of magnesium oxide are compounded with the structure of coal gangue through hot alkali reaction. After the potassium ions and magnesium ions are loaded and accumulated on the surface of coal gangue, the obtained doped coal gangue can not only utilize the oxygen-containing functional groups of coal gangue itself to react with COD in sewage and carbon elements of carbon source in chemical form, so that carbon elements are adsorbed in the doped coal gangue to form certain carbonyl groups, hydrocarbon groups and conjugated double bond compounds, but also the potassium ions and magnesium ions on the surface of doped coal gangue are conducive to forming more micropores and mesopores in coal gangue, increasing the specific surface area of ​​coal gangue, changing the surface structure of coal gangue, providing more adsorption sites, thereby effectively adsorbing and removing COD in sewage.

[0031] 2. In the present invention, polyvinyl alcohol is subjected to radiation treatment to generate free radicals on the surface of the polyvinyl alcohol, which react with the double bonds in glycidyl methacrylate to form a polymer network with good mass transfer performance and abundant active sites, thereby facilitating the adsorption and fixation of nano-ferric oxide in the polymer network formed by polyvinyl alcohol and glycidyl methacrylate. The obtained modified polyvinyl alcohol is used as a fixed carrier raw material for denitrifying bacteria, and can effectively adsorb nitrate ions in sewage with the help of its own polymer network and the effect of nano-ferric oxide, thereby assisting in improving the denitrification efficiency of sewage treatment.

[0032] 3. In the present invention, fixed carrier microspheres are prepared. The fixed carrier microspheres as carriers have good mechanical strength and adsorption properties, which can allow the denitrifying bacteria in the anaerobic activated sludge to attach and fix in the fixed carrier microspheres. Since the doped coal gangue in the fixed carrier microspheres has good COD and carbon source adsorption capacity, and the modified polyvinyl alcohol has good nitrate ion adsorption, it is beneficial to the transmission of nutrients and metabolites and the growth and reproduction of denitrifying bacteria, so that the denitrifying bacteria attached and fixed in the fixed carrier microspheres can utilize the nitrate ions, COD and carbon sources adsorbed in the fixed carrier microspheres, promote the denitrifying bacteria to carry out denitrification and denitrification reactions, efficiently remove COD in sewage and improve the denitrification efficiency of the denitrification reaction. DETAILED DESCRIPTION

[0033] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] Taking the collected urban sewage as an example, the total nitrogen concentration of the urban sewage is 78±13.1 mg / L, and the COD concentration is 142±21.3 mg / L. The urban sewage is used for the sewage treatment objects of Examples 1-3 and Comparative Examples 1-3.

[0035] Example 1

[0036] A process for treating urban sewage based on denitrification and denitrification, specifically comprising the following steps:

[0037] Preparation of doped coal gangue:

[0038] The coal gangue, potassium oxide and magnesium oxide were stirred and mixed in a mass ratio of 15:1:1 and ball-milled to obtain a mixed material, and the mixed material was poured into a sodium hydroxide solution with a concentration of 2 mol / L, and microwaved at 160°C for 40 min, and then stirred and aged at 30°C for 6 h to obtain a mineral liquid mixture;

[0039] The ore-liquid mixture is subjected to high temperature reaction at 220° C. for 3 hours to obtain doped coal gangue.

[0040] Preparation of modified polyvinyl alcohol:

[0041] Nano-iron trioxide and deionized water were stirred and mixed at a mass ratio of 0.3:1, and then ultrasonically treated for 5 minutes to obtain a nano-iron trioxide dispersion. Glycidyl methacrylate and Tween 20 were stirred and mixed at a mass ratio of 40:3 to obtain a mixture. The nano-iron tetroxide dispersion and the mixture were mixed at a mass ratio of 0.5:1 to obtain a reaction solution, which was stored under a nitrogen atmosphere for later use.

[0042] The polyvinyl alcohol was placed in a vacuum sealed bag and irradiated at 10°C for 5 min. The irradiation dose rate was 5 kGy / Pass and the total dose was 25 kGy.

[0043] After the irradiation, the polyvinyl alcohol was immediately taken out from the vacuum sealed bag and quickly added to the reaction solution, and the reaction was stirred at 48° C. for 3 h. After suction filtration, washing and drying, modified polyvinyl alcohol was obtained.

[0044] Preparation of fixed carrier microspheres:

[0045] 24 parts by weight of modified polyvinyl alcohol were added to 120 parts by weight of deionized water, and the mixture was stirred at 95° C. for 15 minutes to obtain a modified polyvinyl alcohol solution. 5 parts by weight of carboxymethyl cellulose and 5 parts by weight of doped coal gangue were added to the modified polyvinyl alcohol solution in sequence under a nitrogen atmosphere, and the mixture was stirred for 60 minutes to obtain a composite gel solution.

[0046] The composite gel solution was injected into a 3 mm spherical mold, and the spherical mold after injection was placed in a refrigerator at -20°C for 12 hours. After molding, the mold was demoulded to obtain gel microspheres. The gel microspheres were added into a 5% by mass calcium chloride saturated boric acid solution and stirred at 28°C for 20 minutes.

[0047] Subsequently, the cross-linked gel microspheres were taken out and placed in a refrigerator at 6° C. for curing for 24 h, and then washed three times with deionized water to obtain fixed carrier microspheres.

[0048] Step S1: sewage pretreatment: the sewage is passed through a coarse screen pool and a fine screen pool in sequence to block floating objects and larger solid particles in the sewage;

[0049] Step S2: Nitrification reaction: inject the pretreated sewage into a nitrification treatment tank, which contains aerobic activated sludge, and introduce air to perform aeration treatment and nitrification reaction on the pretreated sewage. The aerobic activated sludge includes ammonia oxidizing bacteria and nitrite-type denitrifying bacteria, which are used to oxidize ammonia nitrogen in the sewage into nitrate. The nitrification reaction temperature is 28°C, the dissolved oxygen is ≥2mg / L, and the pH is 7.2. The sewage after nitrification treatment is introduced into an intermediate sedimentation tank, and the non-water-soluble substances in the sewage after nitrification treatment are precipitated and filtered to obtain sewage after nitrification treatment;

[0050] Step S3 denitrification and denitrification reaction: inoculate the anaerobic activated sludge into the fixed carrier microspheres, and load the inoculated fixed carrier microspheres into the hollow grid reaction box of the denitrification treatment tank, the anaerobic activated sludge includes denitrifying Thiobacillus, denitrifying Paracoccus, Bacillus subtilis and Pseudomonas, then, inject the sewage that has completed the nitrification treatment into the denitrification treatment tank, add a carbon source into the denitrification treatment tank, the carbon source is methanol, the oxygen-limited system in the denitrification treatment tank monitors the dissolved oxygen concentration in the autotrophic denitrification tank, the denitrification reaction temperature is 32°C, the dissolved oxygen is <5mg / L, the pH is 7.0, the sewage reacts for 3h under continuous slow stirring conditions, and after the denitrification treatment is completed, the effluent water quality is tested.

[0051] Example 2

[0052] A process for treating urban sewage based on denitrification and denitrification, specifically comprising the following steps:

[0053] Preparation of doped coal gangue:

[0054] The coal gangue, potassium oxide and magnesium oxide were stirred and mixed in a mass ratio of 15:1:1 and ball-milled to obtain a mixed material, and the mixed material was poured into a sodium hydroxide solution with a concentration of 2 mol / L, and microwaved at 180°C for 30 min, and then stirred and aged at 36°C for 4 h to obtain a mineral liquid mixture;

[0055] The ore-liquid mixture is subjected to high temperature reaction at 180° C. for 5 hours to obtain doped coal gangue.

[0056] Preparation of modified polyvinyl alcohol:

[0057] Nano-ferric oxide and deionized water were stirred and mixed at a mass ratio of 0.3:1, and then ultrasonically treated for 3 minutes to obtain a nano-ferric oxide dispersion. Glycidyl methacrylate and Tween 20 were stirred and mixed at a mass ratio of 40:3 to obtain a mixture. The nano-ferrous oxide dispersion and the mixture were mixed at a mass ratio of 0.5:1 to obtain a reaction solution, which was stored under a nitrogen atmosphere for later use.

[0058] The polyvinyl alcohol was placed in a vacuum sealed bag and irradiated at 6°C for 5 min. The irradiation dose rate was 5 kGy / Pass and the total dose was 25 kGy.

[0059] After the irradiation, the polyvinyl alcohol was immediately taken out from the vacuum sealed bag and quickly added to the reaction solution, and the reaction was stirred at 42° C. for 4 h. After suction filtration, washing and drying, modified polyvinyl alcohol was obtained.

[0060] Preparation of fixed carrier microspheres:

[0061] 24 parts by weight of modified polyvinyl alcohol were added to 120 parts by weight of deionized water, and the mixture was stirred at 98° C. for 10 minutes to obtain a modified polyvinyl alcohol solution. 5 parts by weight of carboxymethyl cellulose and 5 parts by weight of doped coal gangue were added to the modified polyvinyl alcohol solution in sequence under a nitrogen atmosphere, and the mixture was stirred for 30 minutes to obtain a composite gel solution.

[0062] The composite gel solution was injected into a 3 mm spherical mold, and the spherical mold after injection was placed in a refrigerator at -20°C for 8 h. After molding, the mold was demoulded to obtain gel microspheres. The gel microspheres were added into a 5% by mass calcium chloride saturated boric acid solution and stirred at 24°C for 20 min.

[0063] Subsequently, the cross-linked gel microspheres were taken out and placed in a refrigerator at 3° C. for curing for 12 h, and then washed three times with deionized water to obtain fixed carrier microspheres.

[0064] Step S1: sewage pretreatment: the sewage is passed through a coarse screen pool and a fine screen pool in sequence to block floating objects and larger solid particles in the sewage;

[0065] Step S2: Nitrification reaction: inject the pretreated sewage into a nitrification treatment tank, which contains aerobic activated sludge, and introduce air to perform aeration treatment and nitrification reaction on the pretreated sewage. The aerobic activated sludge includes ammonia oxidizing bacteria and nitrite-type denitrifying bacteria, which are used to oxidize ammonia nitrogen in the sewage into nitrate. The nitrification reaction temperature is 28°C, the dissolved oxygen is ≥2mg / L, and the pH is 7.2. The sewage after nitrification treatment is introduced into an intermediate sedimentation tank, and the non-water-soluble substances in the sewage after nitrification treatment are precipitated and filtered to obtain sewage after nitrification treatment;

[0066] Step S3 denitrification and denitrification reaction: anaerobic activated sludge is inoculated into fixed carrier microspheres, and the inoculated fixed carrier microspheres are loaded into the hollow grid reaction box of the denitrification treatment tank, the anaerobic activated sludge includes denitrifying Thiobacillus, denitrifying Paracoccus, Bacillus subtilis and Pseudomonas, and then the sewage that has completed the nitrification treatment is injected into the denitrification treatment tank, and a carbon source is added to the denitrification treatment tank, the carbon source is methanol, and the oxygen-limited system in the denitrification treatment tank monitors the dissolved oxygen concentration in the autotrophic denitrification tank. The denitrification reaction temperature is 32°C, the dissolved oxygen is <5mg / L, and the pH is 7.0. The sewage reacts for 3h under continuous and slow stirring conditions. After the denitrification treatment is completed, the effluent water quality is tested.

[0067] Example 3

[0068] A process for treating urban sewage based on denitrification and denitrification, specifically comprising the following steps:

[0069] Preparation of doped coal gangue:

[0070] The coal gangue, potassium oxide and magnesium oxide were stirred and mixed in a mass ratio of 10:0.5:0.5 and ball-milled to obtain a mixed material, and the mixed material was poured into a sodium hydroxide solution with a concentration of 2 mol / L, and microwaved at 160°C for 40 min, and then stirred and aged at 30°C for 6 h to obtain a mineral liquid mixture;

[0071] The ore-liquid mixture is subjected to high temperature reaction at 220° C. for 3 hours to obtain doped coal gangue.

[0072] Preparation of modified polyvinyl alcohol:

[0073] Nano-iron trioxide and deionized water were stirred and mixed at a mass ratio of 0.1:1, and then ultrasonically treated for 5 minutes to obtain a nano-iron trioxide dispersion liquid; glycidyl methacrylate and Tween 20 were stirred and mixed at a mass ratio of 40:3 to obtain a mixture; the nano-iron tetroxide dispersion liquid and the mixture were mixed at a mass ratio of 1:1 to obtain a reaction solution, which was stored under a nitrogen atmosphere for later use;

[0074] The polyvinyl alcohol was placed in a vacuum sealed bag and irradiated at 10°C for 5 min. The irradiation dose rate was 5 kGy / Pass and the total dose was 25 kGy.

[0075] After the irradiation, the polyvinyl alcohol was immediately taken out from the vacuum sealed bag and quickly added to the reaction solution, and the reaction was stirred at 48° C. for 3 h. After suction filtration, washing and drying, modified polyvinyl alcohol was obtained.

[0076] Preparation of fixed carrier microspheres:

[0077] 24 parts by weight of modified polyvinyl alcohol were added to 120 parts by weight of deionized water, and the mixture was stirred at 95° C. for 15 minutes to obtain a modified polyvinyl alcohol solution. 3 parts by weight of carboxymethyl cellulose and 3 parts by weight of doped coal gangue were added to the modified polyvinyl alcohol solution in sequence under a nitrogen atmosphere, and the mixture was stirred for 60 minutes to obtain a composite gel solution.

[0078] The composite gel solution was injected into a 3 mm spherical mold, and the spherical mold after injection was placed in a refrigerator at -20°C for 12 hours. After molding, the mold was demoulded to obtain gel microspheres. The gel microspheres were added into a 5% by mass calcium chloride saturated boric acid solution and stirred at 28°C for 20 minutes.

[0079] Subsequently, the cross-linked gel microspheres were taken out and placed in a refrigerator at 6° C. for curing for 24 h, and then washed three times with deionized water to obtain fixed carrier microspheres.

[0080] Step S1: sewage pretreatment: the sewage is passed through a coarse screen pool and a fine screen pool in sequence to block floating objects and larger solid particles in the sewage;

[0081] Step S2: Nitrification reaction: inject the pretreated sewage into a nitrification treatment tank, which contains aerobic activated sludge, and introduce air to perform aeration treatment and nitrification reaction on the pretreated sewage. The aerobic activated sludge includes ammonia oxidizing bacteria and nitrite-type denitrifying bacteria, which are used to oxidize ammonia nitrogen in the sewage into nitrate. The nitrification reaction temperature is 28°C, the dissolved oxygen is ≥2mg / L, and the pH is 7.2. The sewage after nitrification treatment is introduced into an intermediate sedimentation tank, and the non-water-soluble substances in the sewage after nitrification treatment are precipitated and filtered to obtain sewage after nitrification treatment;

[0082] Step S3 denitrification and denitrification reaction: anaerobic activated sludge is inoculated into fixed carrier microspheres, and the inoculated fixed carrier microspheres are loaded into the hollow grid reaction box of the denitrification treatment tank, the anaerobic activated sludge includes denitrifying Thiobacillus, denitrifying Paracoccus, Bacillus subtilis and Pseudomonas, and then the sewage that has completed the nitrification treatment is injected into the denitrification treatment tank, and a carbon source is added to the denitrification treatment tank, the carbon source is methanol, and the oxygen-limited system in the denitrification treatment tank monitors the dissolved oxygen concentration in the autotrophic denitrification tank. The denitrification reaction temperature is 32°C, the dissolved oxygen is <5mg / L, and the pH is 7.0. The sewage reacts for 3h under continuous and slow stirring conditions. After the denitrification treatment is completed, the effluent water quality is tested.

[0083] Comparative Example 1

[0084] Compared with Example 1, the difference of Comparative Example 1 is that, in the preparation of fixed carrier microspheres, the doped coal gangue in the fixed carrier microspheres is replaced with coal gangue, and the other steps remain unchanged. The prepared fixed carrier microspheres are used in the denitrification and denitrification reaction in step S3, and the sewage is subjected to denitrification and denitrification reaction treatment, which is recorded as Comparative Example 1.

[0085] Comparative Example 2

[0086] Compared with Example 1, the difference of Comparative Example 2 is that, in the preparation of the fixed carrier microspheres, the doped coal gangue in the fixed carrier microspheres is removed, and the other steps remain unchanged. The prepared fixed carrier microspheres are used in the denitrification and denitrification reaction in step S3, and the sewage is subjected to denitrification and denitrification reaction treatment, which is recorded as Comparative Example 2.

[0087] Comparative Example 3

[0088] Compared with Example 1, the difference of Comparative Example 3 is that, in the preparation of fixed carrier microspheres, the modified polyvinyl alcohol in the fixed carrier microspheres is replaced by polyvinyl alcohol, and the other steps remain unchanged. The prepared fixed carrier microspheres are used in the denitrification and denitrification reaction in step S3, and the wastewater is subjected to denitrification and denitrification reaction treatment, which is recorded as Comparative Example 3.

[0089] The water quality test results of the effluent after treatment in Examples 1-3 and Comparative Examples 1-3 were statistically analyzed to calculate the removal rate of each pollutant. The removal rate calculation formula is: removal rate (%) = concentration after treatment / initial concentration*100%. The results are shown in Table 1.

[0090] Table 1:

[0091] Group COD removal rate (%) Total nitrogen removal rate (%) Example 1 98.2 96.6 Example 2 97.8 95.9 Example 3 97.5 96.2 Comparative Example 1 89.7 92.1 Comparative Example 2 87.2 90.7 Comparative Example 3 92.1 89.3

[0092] As can be seen from Table 1, the pollutant removal effect of the urban sewage treatment process provided by Examples 1-3 of the present invention is better than that of Comparative Examples 1-3. The COD removal rates after treatment by Examples 1-3 are all above 97%, and the total nitrogen removal rates are all above 95%. This shows that the use of fixed carrier microspheres as carriers to attach and fix denitrifying bacteria in the denitrification reaction step can effectively improve the treatment effect of urban sewage and efficiently remove COD and total nitrogen in sewage.

[0093] The test sewage was prepared with 10 mg / L nitrate and 120 mg / L COD concentration, and the test sewage was divided into 6 samples, 1 L / sample, and 30 g of the fixed carrier microspheres obtained from Examples 1-3 and Comparative Examples 1-3 were taken and put into 6 different samples, respectively, and soaked at room temperature for 1 hour without anaerobic activated sludge inoculation. Subsequently, the fixed carrier microspheres in each sample were fished out, and the pollutant content in each sample was measured, and the removal rate of each pollutant was calculated. The removal rate calculation formula is: Removal rate (%) = concentration after treatment / initial concentration*100%. The results are shown in Table 2.

[0094] Table 2:

[0095] Group COD removal rate (%) Nitrate removal rate (%) Example 1 36.7 31.1 Example 2 34.5 31.6 Example 3 35.2 30.4 Comparative Example 1 30.8 27.5 Comparative Example 2 19.4 22.9 Comparative Example 3 26.1 15.3

[0096] As can be seen from Table 2, the fixed carrier microspheres prepared in Examples 1-3 can be used to adsorb and remove COD and nitrate from the sampled wastewater, and the COD removal rate can reach more than 34% and the nitrate removal rate can reach more than 30%. Compared with the fixed carrier microspheres prepared in Comparative Examples 1-3, the fixed carrier microspheres prepared in Examples 1-3 can more effectively adsorb and remove COD and nitrate from the wastewater.

[0097] The mechanical properties of the fixed carrier microspheres prepared in Examples 1-3 and Comparative Examples 1-3 were tested using an electronic universal testing machine. The test results are shown in Table 3.

[0098] Table 3:

[0099] Group Tensile strength(Mpa) Elongation at break (%) Example 1 1.4 93.3 Example 2 1.6 95.1 Example 3 1.4 92.7 Comparative Example 1 1.1 86.4 Comparative Example 2 0.3 63.2 Comparative Example 3 0.7 80.5

[0100] As can be seen from Table 3, the tensile strength and elongation at break of the fixed carrier microspheres prepared in Examples 1-3 of the present invention are better than those of the fixed carrier microspheres prepared in Comparative Examples 1-3, indicating that the use of doped coal gangue and modified polyvinyl alcohol in the fixed carrier microspheres can effectively improve the overall mechanical properties of the fixed carrier microspheres, ensure that the fixed carrier microspheres maintain their shape and structural integrity in a complex hydraulic environment, reduce the breakage and loss of the fixed carrier microspheres, thereby ensuring that the denitrifying bacteria are not easily lost with the water flow, and are easy to separate and recover from the water after use and treatment.

[0101] It should be understood that those skilled in the art can make improvements or changes based on the above description, and all such improvements and changes should fall within the scope of protection of the appended claims of the present invention. Parts not described in detail in this specification belong to the prior art known to those skilled in the art.

Claims

1. A process for treating urban sewage based on denitrification, characterized in that: The steps include: Step S1: sewage pretreatment: the sewage is passed through a screen tank to block floating objects and larger solid particles in the sewage; Step S2: nitrification reaction: aeration treatment and nitrification reaction are performed on the pretreated sewage, and the sewage after nitrification treatment is passed into an intermediate sedimentation tank to precipitate sludge to obtain sewage after nitrification treatment; Step S3: denitrification and denitrification reaction: introducing the wastewater that has completed the nitrification treatment into the denitrification treatment pool, adding a carbon source and using fixed carrier microspheres to carry out denitrification and denitrification reaction on the wastewater in the denitrification treatment pool. After the denitrification treatment is completed, the effluent water quality is tested; The fixed carrier microspheres are prepared from modified polyvinyl alcohol, carboxymethyl cellulose, doped coal gangue and cross-linking agent as raw materials; Doped coal gangue is obtained by using coal gangue, potassium oxide and magnesium oxide as raw materials, and combining the potassium element of potassium oxide and the magnesium element of magnesium oxide with coal gangue through hot alkali reaction; The modified polyvinyl alcohol is prepared by taking radiation-treated polyvinyl alcohol, glycidyl methacrylate, nano-ferric oxide and deionized water as raw materials.

2. A process for treating urban sewage based on denitrification and denitrification according to claim 1, characterized in that: The preparation of doped coal gangue specifically includes the following steps: The coal gangue, potassium oxide and magnesium oxide are mixed and stirred in a mass ratio of (10-15): (0.1-1): (0.1-1) and ball-milled to obtain a mixed material, the mixed material is poured into a sodium hydroxide solution with a concentration of 2 mol / L, microwave-treated at 150-180° C. for 30-40 min, and then stirred and aged at 28-36° C. for 4-6 h to obtain a mineral liquid mixture; The ore-liquid mixture is reacted at a high temperature of 180-220° C. for 3-5 hours to obtain doped coal gangue.

3. A process for treating urban sewage based on denitrification and denitrification according to claim 1, characterized in that: The preparation of modified polyvinyl alcohol specifically comprises the following steps: The nano-iron trioxide and deionized water are stirred and mixed in a mass ratio of (0.1-0.3):1, and then ultrasonically treated for 3-5 minutes to obtain a nano-iron trioxide dispersion liquid, glycidyl methacrylate and Tween 20 are stirred and mixed in a mass ratio of (10-40):(2-5) to obtain a mixture, and the nano-iron tetroxide dispersion liquid and the mixture are mixed in a mass ratio of (0.2-1):1 to obtain a reaction solution, which is stored under a nitrogen atmosphere for later use; The polyvinyl alcohol is placed in a vacuum sealed bag and irradiated at 6 to 15°C for 5 to 10 minutes; After the irradiation is completed, the polyvinyl alcohol is immediately taken out from the vacuum sealed bag and quickly added to the reaction solution, and the reaction is stirred at 42 to 48° C. for 2 to 4 hours. After suction filtration, washing and drying, the modified polyvinyl alcohol is obtained.

4. A process for treating urban sewage based on denitrification and denitrification according to claim 3, characterized in that: The dose rate of irradiation treatment is 3-8 kGy / Pass, and the total dose is 10-30 kGy.

5. A process for treating urban sewage based on denitrification and denitrification according to claim 1, characterized in that: The preparation of fixed carrier microspheres specifically includes the following steps: 12 to 24 parts by weight of modified polyvinyl alcohol are added to 80 to 150 parts by weight of deionized water, and stirred at 92 to 98° C. for 10 to 15 minutes to obtain a modified polyvinyl alcohol solution. In a nitrogen atmosphere, 1 to 5 parts by weight of carboxymethyl cellulose and 0.6 to 5 parts by weight of doped coal gangue are sequentially added to the modified polyvinyl alcohol solution, and stirred for 30 to 60 minutes to obtain a composite gel solution. The composite gel solution is injected into the mold, and the mold after injection is placed in a refrigerator at -20°C for 8 to 12 hours, and the mold is demolded after molding to obtain gel microspheres, and the gel microspheres are added to the crosslinking agent and stirred at 22 to 30°C for 10 to 20 minutes; Subsequently, the cross-linked gel microspheres were taken out and placed in a refrigerator at 3 to 6° C. for refrigeration and solidification for 12 to 24 hours, and then washed with deionized water for 2 to 3 times to obtain fixed carrier microspheres.

6. A process for treating urban sewage based on denitrification and denitrification according to claim 5, characterized in that: The cross-linking agent is a 5% calcium chloride saturated boric acid solution.

7. A process for treating urban sewage based on denitrification and denitrification according to claim 6, characterized in that: The mold is a spherical mold with a diameter of 3 to 5 mm.

8. A process for treating urban sewage based on denitrification and denitrification according to claim 1, characterized in that: The nitrification reaction temperature is 18-30°C, the dissolved oxygen is ≥2 mg / L, and the pH is 7-8.

9. A process for treating urban sewage based on denitrification and denitrification according to claim 1, characterized in that: The denitrification reaction temperature is 20-35°C, the dissolved oxygen is <5 mg / L, and the pH is 7-7.

5.

10. A process for treating urban sewage based on denitrification and denitrification according to claim 1, characterized in that: The carbon source is at least one of methanol, sodium acetate or glucose.