Economical efficient sewage treatment method based on terminal denitrification

Abstract

The invention relates to an economical efficient sewage treatment method based on end denitrification, and belongs to the technical field of sewage treatment. In order to solve the problems of low efficiency and high medicament cost of the existing sewage treatment denitrification process, the invention provides an economical efficient sewage treatment method based on end denitrification, return sludge of a secondary sedimentation tank is introduced into a mixed reaction zone of an efficient clarification tank to be mixed with incoming water, sodium acetate is added into the mixed reaction zone to perform denitrification reaction for 10-30 minutes, and the denitrification reaction is performed for 10-30 minutes; a mud-water mixture formed by reaction enters a settling zone of the efficient clarification tank, floc in the mud-water mixture sinks to the bottom of the tank to form sludge, and clear water on the upper layer is discharged out of the efficient clarification tank through an effluent weir. According to the invention, the efficient clarification tank is used for transformation, denitrification flora of a biochemical system is used for denitrification, and 80% of denitrification reaction can be completed by staying for 10 minutes at the shortest time, so that the denitrification efficiency is remarkably improved, and on the premise of ensuring that the total nitrogen index of effluent is stable and reaches the standard, accurate dosing is realized, and the medicament cost is saved.

Description

Technical Field

[0001] The invention belongs to the technical field of sewage treatment, and in particular relates to an economical and efficient sewage treatment method based on terminal denitrification. Background Art

[0002] With the increasing requirements for environmental protection and increasingly stringent sewage treatment emission indicators, traditional sewage treatment processes have certain limitations in terms of treatment efficiency, environmental adaptability, floor space and operating costs. Especially in the denitrification process, the traditional activated sludge method requires a large amount of carbon source to be added to the anoxic system after the biochemical reaction for denitrification reaction. The retention time of biochemical reaction and other monomers is usually more than 24 hours, and the stability of the effluent cannot be guaranteed during this period. In addition, in order to ensure that the emission indicators meet the standards, it is often necessary to add excessive and outdated drugs, which wastes a lot of drugs and increases the operating costs of sewage treatment.

[0003] In order to further reduce the nitrogen and phosphorus content in the sewage after the secondary sedimentation tank treatment, the patent application "A method for treating domestic sewage" with publication number CN111995172A treats the sewage in a coagulation tank and a denitrification deep bed filter after the secondary sedimentation tank. In this method, the denitrification deep bed filter needs to be designed and constructed when the plant is built. Due to the limited amount of unit bacteria, a large space is required to fully react with the incoming water, which increases the floor space of sewage treatment. In addition, the sewage needs to stay in the denitrification deep bed filter for 30 to 50 minutes to fully react, which reduces the denitrification efficiency. In addition, the sodium acetate added in the coagulation tank in this method must first react with the dissolved oxygen in the sewage in the secondary sedimentation tank, and the remaining part will undergo denitrification reaction in the denitrification deep bed filter, which greatly increases the cost of using the reagents.

[0004] How to further improve the denitrification efficiency of the sewage treatment process while ensuring that all effluent indicators meet discharge standards and save the cost of chemical addition remains an urgent problem to be solved in this field. Summary of the invention

[0005] In order to solve the problems of low efficiency and high reagent cost in the existing sewage treatment denitrification process, the present invention provides an economical and efficient sewage treatment method based on terminal denitrification.

[0006] The technical solution of the present invention:

[0007] An economical and efficient sewage treatment method based on terminal denitrification, wherein the return sludge from the secondary sedimentation tank is introduced into the mixed reaction zone of the high-efficiency clarification tank and mixed with the incoming water, sodium acetate is added to the mixed reaction zone for denitrification reaction, and the reaction time is 10 to 30 minutes. The mud-water mixture formed by the reaction enters the sedimentation zone of the high-efficiency clarification tank, and the flocs in the mud-water mixture sink to the bottom of the tank to form sludge, and the clear water on the upper layer is discharged from the high-efficiency clarification tank through the outlet weir.

[0008] Furthermore, the concentration of the return sludge from the secondary sedimentation tank is 15000-30000 mg / L, and the return sludge from the secondary sedimentation tank is mixed with incoming water at a volume ratio of 1:5-1:10, so that the sludge concentration in the mixed reaction zone reaches 3000-8000 mg / L.

[0009] Furthermore, the dissolved oxygen after the return sludge from the secondary sedimentation tank is mixed with the incoming water is less than 1 mg / L.

[0010] Furthermore, the bacterial concentration of the denitrifying bacteria contained in the return sludge of the secondary sedimentation tank is 3000-8000 mg / L.

[0011] Furthermore, the microbial strains with denitrification function contained in the return sludge of the secondary sedimentation tank include Pseudomonas numbered BNCC193134, Bacillus subtilis numbered BNCC193111, Acidophilus oligotrophicus numbered BNCC190126, Bacillus brevis numbered BNCC190743, Photobacillus luminescens numbered 1.12159 and Bacillus subtilis numbered 18086.

[0012] Furthermore, the amount of sodium acetate added is 50 to 400 ppm.

[0013] Furthermore, the mixed reaction zone also includes a process of adding iron salt to remove phosphorus.

[0014] Furthermore, the iron salt is ferric chloride, and the added amount of the ferric chloride is 30 to 100 ppm.

[0015] Furthermore, the mixing reaction zone is provided with a stirring device to promote rapid mixing of the return sludge from the secondary sedimentation tank and the incoming water.

[0016] Furthermore, the sedimentation zone is provided with inclined plates or inclined tubes to increase the sedimentation area and shorten the sedimentation distance of the particles, thereby improving the sedimentation efficiency.

[0017] Furthermore, the sludge that sinks to the bottom of the pool is concentrated in the sludge concentration area, and the sludge concentration area is provided with a sludge discharge pump to continuously return the precipitated sludge to the biochemical system for reuse to prevent sludge leakage in the sludge concentration area.

[0018] Beneficial effects of the present invention:

[0019] The present invention utilizes a high-efficiency clarifier for transformation, and adds a denitrification function on the basis of its original phosphorus removal and suspended solids removal. The present invention does not need to set up a denitrification tank separately for the cultivation of microbial flora, but introduces the return sludge from the secondary sedimentation tank into the clarification tank, and utilizes the denitrification flora of the biochemical system for denitrification, which not only can take the flora at any time but also can keep the same strain with the biochemical system. In the terminal denitrification process provided by the present invention, the sewage can complete 80% of the denitrification reaction in the mixed reaction zone of the clarification tank for a minimum stay of 10 minutes, and complete 87% of the denitrification reaction in 30 minutes, which significantly improves the denitrification efficiency. The terminal denitrification process of the present invention utilizes the low dissolved oxygen characteristics of the denitrification flora of the biochemical system. After the incoming water and the flora are neutralized, the dissolved oxygen is less than 1 mg / L, so that the added sodium acetate will save the part consumed by the dissolved oxygen, and the added agent will be fully utilized in the denitrification reaction. Under the premise of ensuring that the total nitrogen index of the effluent is stable and up to standard, it has the timeliness of process control and the accuracy of the dosage, saves the cost of adding agents, and reduces the operating cost of sewage treatment.

[0020] The economical and efficient sewage treatment method based on terminal denitrification provided by the present invention has controllable performance of total nitrogen data in sewage treatment to ensure that the total nitrogen in the effluent meets the standard stably, and prevents the effluent from exceeding the standard due to the long time-effect of adding reagents in the original activated sludge method. The method can quickly reduce the total nitrogen index of the total effluent within 1 to 2 hours, and can accurately add drugs without being affected by the quality and quantity of the influent water, and the transformation investment cost is low. Since the minimum residence time can be controlled to 10 minutes, even if there is no clarification tank on site, a small reaction tank can be built separately. DETAILED DESCRIPTION

[0021] The technical solution of the present invention is further described below in conjunction with the embodiments, but it is not limited thereto. Any modification or equivalent replacement of the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention shall be included in the protection scope of the present invention. The process equipment or devices not specifically noted in the following embodiments are all conventional equipment or devices in the art. If not specifically specified, the raw materials used in the embodiments of the present invention can be obtained commercially; if not specifically specified, the technical means used in the embodiments of the present invention are all conventional means well known to those skilled in the art.

[0022] Example 1

[0023] This embodiment provides an economical and efficient sewage treatment method based on terminal denitrification.

[0024] In this embodiment, the return sludge from the secondary sedimentation tank is introduced into the mixing reaction zone of the clarification tank to mix with the incoming water. The concentration of the return sludge from the secondary sedimentation tank is 30000 mg / L, and it is mixed with the incoming water at a volume ratio of 1:4. The mixing reaction zone is provided with a stirring device to promote the rapid mixing of the return sludge from the secondary sedimentation tank and the incoming water. The nitrate nitrogen concentration in the incoming water is measured to be 6.92 mg / L, and the COD (chemical oxygen demand) is 20.4 mg / L.

[0025] After mixing, the sludge concentration in the mixed reaction zone reaches 6000 mg / L, the dissolved oxygen after mixing is less than 1 mg / L, and the concentration of denitrifying bacteria contained in the return sludge from the secondary sedimentation tank and the incoming water is 6000 mg / L. The microbial strains with denitrification contained in the return sludge from the secondary sedimentation tank include Pseudomonas numbered BNCC193134, Bacillus subtilis numbered BNCC193111, Acidophilus oligotrophomonas numbered BNCC190126, Bacillus brevis numbered BNCC190743, Photobacillus aquaticus numbered 1.12159, and Bacillus subtilis numbered 18086.

[0026] 50ppm of solid sodium acetate was added to the mixed reaction zone for denitrification reaction, and ferric chloride was added for phosphorus removal. The reaction time was 10min. The mud-water mixture formed by the reaction entered the sedimentation zone of the clarification tank. The sedimentation zone was equipped with inclined plates to increase the sedimentation area and shorten the sedimentation distance of the particles, thereby improving the sedimentation efficiency.

[0027] The flocs in the mud-water mixture sank to the bottom of the pool to form sludge, and the clear water on the upper layer was discharged from the clarification tank through the outlet weir. The nitrate nitrogen in the water was 2.13 mg / L and the COD was 14.8 mg / L.

[0028] Example 2

[0029] This embodiment provides an economical and efficient sewage treatment method based on terminal denitrification.

[0030] In this embodiment, the return sludge from the secondary sedimentation tank is introduced into the mixing reaction zone of the clarification tank to mix with the incoming water. The concentration of the return sludge from the secondary sedimentation tank is 30000 mg / L, and it is mixed with the incoming water at a volume ratio of 1:4. The mixing reaction zone is provided with a stirring device to promote the rapid mixing of the return sludge from the secondary sedimentation tank and the incoming water. The nitrate nitrogen concentration in the incoming water is measured to be 6.92 mg / L, and the COD (chemical oxygen demand) is 20.4 mg / L.

[0031] After mixing, the sludge concentration in the mixed reaction zone reaches 6000 mg / L, the dissolved oxygen after mixing is less than 1 mg / L, and the concentration of denitrifying bacteria contained in the return sludge from the secondary sedimentation tank and the incoming water is 6000 mg / L. The microbial strains with denitrification contained in the return sludge from the secondary sedimentation tank include Pseudomonas numbered BNCC193134, Bacillus subtilis numbered BNCC193111, Acidophilus oligotrophomonas numbered BNCC190126, Bacillus brevis numbered BNCC190743, Photobacillus aquaticus numbered 1.12159, and Bacillus subtilis numbered 18086.

[0032] 50ppm of solid sodium acetate was added to the mixed reaction zone for denitrification reaction, and ferric chloride was added for phosphorus removal. The reaction time was 20min. The mud-water mixture formed by the reaction entered the sedimentation zone of the clarification tank. The sedimentation zone was equipped with inclined plates to increase the sedimentation area and shorten the sedimentation distance of the particles, thereby improving the sedimentation efficiency.

[0033] The flocs in the mud-water mixture sank to the bottom of the pool to form sludge, and the clear water on the upper layer was discharged from the clarification tank through the outlet weir. The nitrate nitrogen concentration in the water was measured to be 1.83 mg / L.

[0034] Example 3

[0035] This embodiment provides an economical and efficient sewage treatment method based on terminal denitrification.

[0036] In this embodiment, the return sludge from the secondary sedimentation tank is introduced into the mixing reaction zone of the clarification tank to mix with the incoming water. The concentration of the return sludge from the secondary sedimentation tank is 30000 mg / L, and it is mixed with the incoming water at a volume ratio of 1:4. The mixing reaction zone is provided with a stirring device to promote the rapid mixing of the return sludge from the secondary sedimentation tank and the incoming water. The nitrate nitrogen concentration in the incoming water is measured to be 6.92 mg / L, and the COD (chemical oxygen demand) is 20.4 mg / L.

[0037] After mixing, the sludge concentration in the mixed reaction zone reaches 6000 mg / L, the dissolved oxygen after mixing is less than 1 mg / L, and the concentration of denitrifying bacteria contained in the return sludge from the secondary sedimentation tank and the incoming water is 6000 mg / L. The microbial strains with denitrification contained in the return sludge from the secondary sedimentation tank include Pseudomonas numbered BNCC193134, Bacillus subtilis numbered BNCC193111, Acidophilus oligotrophomonas numbered BNCC190126, Bacillus brevis numbered BNCC190743, Photobacillus aquaticus numbered 1.12159, and Bacillus subtilis numbered 18086.

[0038] 50ppm of solid sodium acetate was added to the mixed reaction zone for denitrification reaction, and ferric chloride was added for phosphorus removal. The reaction time was 30min. The mud-water mixture formed by the reaction entered the sedimentation zone of the clarification tank. The sedimentation zone was equipped with inclined plates to increase the sedimentation area and shorten the sedimentation distance of the particles, thereby improving the sedimentation efficiency.

[0039] The flocs in the mud-water mixture sank to the bottom of the pool to form sludge, and the clear water on the upper layer was discharged from the clarification tank through the outlet weir. The nitrate nitrogen concentration in the water was measured to be 1.76 mg / L.

[0040] Comparative Example 1

[0041] This comparative example provides an economical and efficient sewage treatment method based on terminal denitrification.

[0042] In this comparative example, the return sludge from the secondary sedimentation tank is introduced into the mixing reaction zone of the clarification tank to mix with the incoming water. The concentration of the return sludge from the secondary sedimentation tank is 30000 mg / L, and it is mixed with the incoming water at a volume ratio of 1:4. The mixing reaction zone is equipped with a stirring device to promote the rapid mixing of the return sludge from the secondary sedimentation tank and the incoming water. The nitrate nitrogen concentration in the incoming water is 6.92 mg / L, and the COD (chemical oxygen demand) is 20.4 mg / L.

[0043] After mixing, the sludge concentration in the mixed reaction zone reaches 6000 mg / L, the dissolved oxygen after mixing is less than 1 mg / L, and the concentration of denitrifying bacteria contained in the return sludge from the secondary sedimentation tank and the incoming water is 6000 mg / L. The microbial strains with denitrification contained in the return sludge from the secondary sedimentation tank include Pseudomonas numbered BNCC193134, Bacillus subtilis numbered BNCC193111, Acidophilus oligotrophomonas numbered BNCC190126, Bacillus brevis numbered BNCC190743, Photobacillus aquaticus numbered 1.12159, and Bacillus subtilis numbered 18086.

[0044] 50ppm of solid sodium acetate was added to the mixed reaction zone for denitrification reaction, and ferric chloride was added for phosphorus removal. The reaction time was 60min. The mud-water mixture formed by the reaction entered the sedimentation zone of the clarification tank. The sedimentation zone was equipped with inclined plates to increase the sedimentation area and shorten the sedimentation distance of the particles, thereby improving the sedimentation efficiency.

[0045] The flocs in the mud-water mixture sank to the bottom of the pool to form sludge, and the clear water on the upper layer was discharged from the clarification tank through the outlet weir. The nitrate nitrogen concentration in the water was measured to be 1.02 mg / L.

[0046] Compared with Comparative Example 1, Examples 1 to 3 can rapidly carry out the denitrification reaction, with 80% of the denitrification reaction completed within 10 minutes and 87% completed within 30 minutes.

[0047] Example 4

[0048] This embodiment provides an economical and efficient sewage treatment method based on terminal denitrification.

[0049] In this embodiment, the return sludge from the secondary sedimentation tank is introduced into the mixing reaction zone of the clarification tank to mix with the incoming water. The concentration of the return sludge from the secondary sedimentation tank is 30000 mg / L, and it is mixed with the incoming water at a volume ratio of 1:4. The mixing reaction zone is provided with a stirring device to promote the rapid mixing of the return sludge from the secondary sedimentation tank and the incoming water. The nitrate nitrogen concentration in the incoming water is measured to be 6.92 mg / L, and the COD (chemical oxygen demand) is 20.4 mg / L.

[0050] After mixing, the sludge concentration in the mixed reaction zone reaches 6000 mg / L, the dissolved oxygen after mixing is less than 1 mg / L, and the concentration of denitrifying bacteria contained in the return sludge from the secondary sedimentation tank and the incoming water is 6000 mg / L. The microbial strains with denitrification contained in the return sludge from the secondary sedimentation tank include Pseudomonas numbered BNCC193134, Bacillus subtilis numbered BNCC193111, Acidophilus oligotrophomonas numbered BNCC190126, Bacillus brevis numbered BNCC190743, Photobacillus aquaticus numbered 1.12159, and Bacillus subtilis numbered 18086.

[0051] 100ppm of solid sodium acetate was added to the mixed reaction zone for denitrification reaction, and ferric chloride was added for phosphorus removal. The reaction time was 10min. The mud-water mixture formed by the reaction entered the sedimentation zone of the clarification tank. The sedimentation zone was equipped with inclined plates to increase the sedimentation area and shorten the sedimentation distance of the particles, thereby improving the sedimentation efficiency.

[0052] The flocs in the mud-water mixture sank to the bottom of the pool to form sludge, and the clear water on the upper layer was discharged from the clarification tank through the outlet weir. The nitrate nitrogen concentration in the water was measured to be 0.36 mg / L and the COD was 18.8 mg / L.

[0053] Example 5

[0054] This embodiment provides an economical and efficient sewage treatment method based on terminal denitrification.

[0055] In this embodiment, the return sludge from the secondary sedimentation tank is introduced into the mixing reaction zone of the clarification tank to mix with the incoming water. The concentration of the return sludge from the secondary sedimentation tank is 30000 mg / L, and it is mixed with the incoming water at a volume ratio of 1:4. The mixing reaction zone is provided with a stirring device to promote the rapid mixing of the return sludge from the secondary sedimentation tank and the incoming water. The nitrate nitrogen concentration in the incoming water is measured to be 6.92 mg / L, and the COD (chemical oxygen demand) is 20.4 mg / L.

[0056] After mixing, the sludge concentration in the mixed reaction zone reaches 6000 mg / L, the dissolved oxygen after mixing is less than 1 mg / L, and the concentration of denitrifying bacteria contained in the return sludge from the secondary sedimentation tank and the incoming water is 6000 mg / L. The microbial strains with denitrification contained in the return sludge from the secondary sedimentation tank include Pseudomonas numbered BNCC193134, Bacillus subtilis numbered BNCC193111, Acidophilus oligotrophomonas numbered BNCC190126, Bacillus brevis numbered BNCC190743, Photobacillus aquaticus numbered 1.12159, and Bacillus subtilis numbered 18086.

[0057] 200ppm of solid sodium acetate was added to the mixed reaction zone for denitrification reaction, and ferric chloride was added for phosphorus removal. The reaction time was 10min. The mud-water mixture formed by the reaction entered the sedimentation zone of the clarification tank. The sedimentation zone was equipped with inclined plates to increase the sedimentation area and shorten the sedimentation distance of the particles, thereby improving the sedimentation efficiency.

[0058] The flocs in the mud-water mixture sank to the bottom of the pool to form sludge, and the clear water on the upper layer was discharged from the clarification tank through the outlet weir. The nitrate nitrogen concentration in the water was measured to be 0.21 mg / L and the COD was 27.2 mg / L.

[0059] Example 6

[0060] This embodiment provides an economical and efficient sewage treatment method based on terminal denitrification.

[0061] In this embodiment, the return sludge from the secondary sedimentation tank is introduced into the mixing reaction zone of the clarification tank to mix with the incoming water. The concentration of the return sludge from the secondary sedimentation tank is 30000 mg / L, and it is mixed with the incoming water at a volume ratio of 1:4. The mixing reaction zone is provided with a stirring device to promote the rapid mixing of the return sludge from the secondary sedimentation tank and the incoming water. The nitrate nitrogen concentration in the incoming water is measured to be 6.92 mg / L, and the COD (chemical oxygen demand) is 20.4 mg / L.

[0062] After mixing, the sludge concentration in the mixed reaction zone reaches 6000 mg / L, the dissolved oxygen after mixing is less than 1 mg / L, and the concentration of denitrifying bacteria contained in the return sludge from the secondary sedimentation tank and the incoming water is 6000 mg / L. The microbial strains with denitrification contained in the return sludge from the secondary sedimentation tank include Pseudomonas numbered BNCC193134, Bacillus subtilis numbered BNCC193111, Acidophilus oligotrophomonas numbered BNCC190126, Bacillus brevis numbered BNCC190743, Photobacillus aquaticus numbered 1.12159, and Bacillus subtilis numbered 18086.

[0063] 300ppm of solid sodium acetate was added to the mixed reaction zone for denitrification reaction, and ferric chloride was added for phosphorus removal. The reaction time was 10min. The mud-water mixture formed by the reaction entered the sedimentation zone of the clarification tank. The sedimentation zone was equipped with inclined plates to increase the sedimentation area and shorten the sedimentation distance of the particles, thereby improving the sedimentation efficiency.

[0064] The flocs in the mud-water mixture sank to the bottom of the pool to form sludge, and the clear water on the upper layer was discharged from the clarification tank through the outlet weir. The nitrate nitrogen concentration in the water was measured to be 0.36 mg / L and the COD was 36.8 mg / L.

[0065] Example 7

[0066] This embodiment provides an economical and efficient sewage treatment method based on terminal denitrification.

[0067] In this embodiment, the return sludge from the secondary sedimentation tank is introduced into the mixing reaction zone of the clarification tank to mix with the incoming water. The concentration of the return sludge from the secondary sedimentation tank is 30000 mg / L, and it is mixed with the incoming water at a volume ratio of 1:4. The mixing reaction zone is provided with a stirring device to promote the rapid mixing of the return sludge from the secondary sedimentation tank and the incoming water. The nitrate nitrogen concentration in the incoming water is measured to be 6.92 mg / L, and the COD (chemical oxygen demand) is 20.4 mg / L.

[0068] After mixing, the sludge concentration in the mixed reaction zone reaches 6000 mg / L, the dissolved oxygen after mixing is less than 1 mg / L, and the concentration of denitrifying bacteria contained in the return sludge from the secondary sedimentation tank and the incoming water is 6000 mg / L. The microbial strains with denitrification contained in the return sludge from the secondary sedimentation tank include Pseudomonas numbered BNCC193134, Bacillus subtilis numbered BNCC193111, Acidophilus oligotrophomonas numbered BNCC190126, Bacillus brevis numbered BNCC190743, Photobacillus aquaticus numbered 1.12159, and Bacillus subtilis numbered 18086.

[0069] 400ppm of solid sodium acetate was added to the mixed reaction zone for denitrification reaction, and ferric chloride was added for phosphorus removal. The reaction time was 10min. The mud-water mixture formed by the reaction entered the sedimentation zone of the clarification tank. The sedimentation zone was equipped with inclined plates to increase the sedimentation area and shorten the sedimentation distance of the particles, thereby improving the sedimentation efficiency.

[0070] The flocs in the mud-water mixture sank to the bottom of the pool to form sludge, and the clear water on the upper layer was discharged from the clarification tank through the outlet weir. The nitrate nitrogen concentration in the water was measured to be 0.27 mg / L and the COD was 47.6 mg / L.

[0071] As shown in Examples 4 to 7, 100 ppm of sodium acetate was added and stirred for 10 minutes to substantially remove all nitrate nitrogen.

[0072] Example 8

[0073] The Nongkai District Sewage Treatment Plant in Tai'an County, Anshan City, Liaoning Province adopts AAO process + deep treatment (high-efficiency clarification tank + fiber turntable + contact disinfection tank), with a designed capacity of 30,000 tons / day and an actual processing capacity of 15,000 tons / day. The effluent complies with Level A of the "Pollutant Discharge Standard for Urban Sewage Treatment Plants" (GB18918-2002).

[0074] The sewage treatment plant belongs to the agricultural park sewage treatment plant, which treats upstream pre-treated sewage. The types of enterprises involved include slaughterhouse wastewater, food processing wastewater, etc. After pre-treatment, the sewage is characterized by high total phosphorus and total nitrogen, unstable COD, and a carbon-nitrogen ratio of 2 when low and 10 when high. The sewage is the COD after pre-treatment and has low biodegradability. Since the upstream enterprises are not in continuous production, the 10 major enterprises that discharge water have different discharge volumes and different discharge times according to production plans. The water quality and water volume of the mixed water discharged into the sewage treatment plant fluctuate greatly. The sewage treatment plant is not designed with conditioning tanks and homogenization tanks, which has a great impact on the water quality and water volume of the sewage treatment plant. In order to ensure that the total nitrogen in the effluent is stable and meets the standards, a large amount of carbon source needs to be added in the anoxic section to ensure that the total nitrogen in the effluent is stable and meets the standards.

[0075] The average influent COD of the sewage treatment plant is 100 mg / L, total nitrogen is 30 mg / L, total phosphorus is 5 mg / L, and ammonia nitrogen is about 10 mg / L. Without adding carbon source, the effluent total nitrogen is about 18 mg / L. The total phosphorus can be stably controlled below 0.3 mg / L through deep dosing in the high-efficiency clarification tank. The effluent COD is 15 mg / L, and the effluent ammonia nitrogen is 0.5 mg / L.

[0076] In order to ensure that the total nitrogen in the effluent reaches the Class A standard of the Pollutant Discharge Standard for Urban Sewage Treatment Plants (GB18918-2002), a carbon source is added in the anoxic section. The agent added is a carbon source with a COD content of 600,000 commonly found on the market, which is added at 100ppm, with a daily dosage of about 1.5 to 2 tons and a monthly dosage of about 45 to 60 tons. Moreover, when it is found that the effluent index exceeds 12mg / L, the influent carbon source will be added to 150ppm. The retention time of the biochemical pool is about 24 hours, and the retention time of the secondary sedimentation tank and deep treatment is about 5 hours. When the effluent index drops to 10mg / L, it will be about 30 hours. If the total nitrogen continues to rise during this period, there will be no other way, so it can only be analyzed based on the influent water quality and water volume. It is safest to control the total nitrogen in the effluent at 10mg / L on a daily basis. Due to large fluctuations in influent volume and quality, it is necessary to control the effluent total nitrogen at around 10 mg / L, and reserve system buffer space to prevent the effluent total nitrogen from exceeding the standard due to influent fluctuations and long dosing time.

[0077] The sewage treatment plant was remodeled according to the economical and efficient sewage treatment method based on terminal denitrification provided by the present invention. The terminal denitrification unit after the modification includes a mixed reaction zone, a transition zone between the mixed reaction zone and the sedimentation zone, and a sedimentation zone. After adding solid ammonium acetate at 100 ppm, the nitrate nitrogen concentration in the mixed reaction zone decreased from 4.12 mg / L to 1.02 mg / L 30 minutes later. After 60 minutes, the nitrate nitrogen concentration in the mixed reaction zone was 1.15 mg / L, the nitrate nitrogen concentration in the transition zone was 0.69 mg / L, and the nitrate nitrogen concentration in the sedimentation zone was 1.52 mg / L. At this point, the water passed through the fiber turntable and was directly discharged after disinfection.

[0078] After the plant used the terminal denitrification process, several indicators were compared:

[0079] 1. Timeliness:

[0080] The original activated sludge method adds carbon sources in the anoxic section to remove total nitrogen. After adding the drug in the anoxic section, it takes 20 to 30 hours to reach the bottom outlet, during which time it is easy to cause the effluent to exceed the standard.

[0081] After using the terminal denitrification process, the carbon source will be added to the effluent 1 hour later to ensure that the effluent can stably meet the discharge standards.

[0082] 2. Economical:

[0083] Due to the large fluctuations in the water quality and water volume of the plant, the original activated sludge process added carbon sources in the anoxic section to remove total nitrogen. After adding the agent in the anoxic section, it takes 20 to 30 hours to reach the bottom outlet. The total nitrogen in the effluent needs to be controlled at around 10 mg / l, and a buffer space is reserved for the system to prevent the total nitrogen in the effluent from exceeding the standard due to the fluctuation of the influent and the long timeliness of the agent addition. About 45 to 60 tons of carbon sources are added each month.

[0084] After using the end-point denitrification process, the dosage of the agent can be completely accurate. The dosage of the agent is changed according to the online changes of the effluent at all times to ensure that the total nitrogen in the effluent is stable and meets the standard. The monthly carbon source dosage is only about 10 tons, saving nearly 80%.

Claims

1. An economical and efficient sewage treatment method based on terminal denitrification, characterized in that: The return sludge from the secondary sedimentation tank is introduced into the mixing reaction zone of the high-efficiency clarification tank and mixed with the incoming water. Sodium acetate is added to the mixing reaction zone for denitrification reaction. The reaction time is 10 to 30 minutes. The mud-water mixture formed by the reaction enters the sedimentation zone of the high-efficiency clarification tank. The flocs in the mud-water mixture sink to the bottom of the tank to form sludge. The clear water on the upper layer is discharged from the high-efficiency clarification tank through the outlet weir.

2. According to claim 1, an economical and efficient sewage treatment method based on terminal denitrification is characterized in that: The concentration of the return sludge from the secondary sedimentation tank is 15000-30000 mg / L. The return sludge from the secondary sedimentation tank is mixed with incoming water at a volume ratio of 1:5-1:10, so that the sludge concentration in the mixed reaction zone reaches 3000-8000 mg / L.

3. An economical and efficient sewage treatment method based on terminal denitrification according to claim 1 or 2, characterized in that: The dissolved oxygen in the secondary sedimentation tank return sludge and the incoming water after mixing is less than 1 mg / L.

4. According to claim 3, an economical and efficient sewage treatment method based on terminal denitrification is characterized in that: The concentration of denitrifying bacteria contained in the mixture of the return sludge from the secondary sedimentation tank and the incoming water is 3000-8000 mg / L.

5. According to claim 4, an economical and efficient sewage treatment method based on terminal denitrification is characterized in that: The amount of sodium acetate added is 50 to 400 ppm.

6. The economical and efficient sewage treatment method based on terminal denitrification according to claim 5, characterized in that: The mixed reaction zone also includes a treatment for adding iron salts to remove phosphorus.

7. An economical and efficient sewage treatment method based on terminal denitrification according to claim 6, characterized in that: The iron salt is ferric chloride, and the added amount of the ferric chloride is 30-100 ppm.

8. The economical and efficient sewage treatment method based on terminal denitrification according to claim 7, characterized in that: The mixing reaction zone is provided with a stirring device.

9. The economical and efficient sewage treatment method based on terminal denitrification according to claim 8, characterized in that: The sedimentation zone is provided with inclined plates or inclined tubes.

10. The economical and efficient sewage treatment method based on terminal denitrification according to claim 9, characterized in that: The sludge that sinks to the bottom of the pool is concentrated in the sludge concentration area, and the sludge concentration area is provided with a sludge discharge pump to continuously return the precipitated sludge to the biochemical system for reuse.