Eutrophic river and lake water body treatment method and treatment system

Abstract

The invention belongs to the technical field of sewage treatment, and discloses an eutrophic river and lake water body treatment method and system.The method comprises the steps that a bypass is arranged, a to-be-treated river and lake water body is extracted for oxygen elimination treatment, and a low-oxygen water body is obtained; the low-oxygen water body is introduced into a denitrification unit for autotrophic denitrification nitrogen removal treatment, and a denitrified water body is obtained; and carrying out magnetic coagulation dephosphorization treatment on the denitrified water body to obtain the denitrified and dephosphorized water body. The system comprises a filtering unit, an oxygen elimination unit, a nitrogen removal unit and a phosphorus removal unit which are arranged in sequence, the oxygen elimination unit is used for reducing the dissolved oxygen concentration of the river and lake water body; the nitrogen removal unit is an autotrophic denitrification nitrogen removal unit, and autotrophic denitrification microorganisms are adopted for biological nitrogen removal; and the phosphorus removal unit is a magnetic coagulation phosphorus removal unit. The method and the system are suitable for eutrophic river and lake water body treatment, low in treatment cost, small in influence of water quality fluctuation and high in adaptability.

Description

Technical Field

[0001] The invention belongs to the technical field of sewage treatment, and specifically relates to a method and system for treating eutrophic river and lake water. Background Art

[0002] With the rapid development of social economy, a large number of agricultural fertilizers and pesticides rich in nitrogen and phosphorus are used, entering rivers and lakes through farmland surface runoff and underground seepage, causing nitrate and phosphate pollution in some natural water bodies. Excessive nitrogen and phosphorus elements in water bodies will cause eutrophication of water bodies, leading to water deterioration and the emission of greenhouse gas N2O, threatening the safety of water bodies and ecological environment.

[0003] At present, the methods for removing nitrogen and phosphorus from rivers and lakes are mainly divided into biological methods, physical methods and chemical methods. Among them, the biological method mainly uses water hyacinth, duckweed and other aquatic plants and floating plants to remove nitrogen and phosphorus in the water body and repair and purify the water quality; although it has a certain effect, it is slow to take effect, and because most aquatic plants are difficult to generate direct economic benefits, they are prone to sequelae. The physical method mainly reduces nitrogen and phosphorus in the water body through filtration and bottom mud cleaning, which has the problems of high cost and high technical difficulty. If it is not mastered well, it may lead to the destruction of the N and P balance of the water body and make the water quality worse. The chemical method mainly involves spreading adsorbents or coagulants, etc., to remove pollutants such as nitrogen and phosphorus through adsorption or precipitation; although it takes effect quickly and the effect is obvious, it is difficult to accurately control the dosage and the chemical sludge produced is difficult to remove, and there is a risk of secondary pollution.

[0004] The above methods are mainly in-situ repair methods. Although bypass repair methods have been reported, they have problems such as high treatment costs, great impact from water quality fluctuations, and difficulty in ensuring treated water quality. They have poor adaptability and are difficult to promote and apply on a large scale in actual production. Summary of the invention

[0005] In view of the deficiencies in the above-mentioned prior art, the object of the present invention is to provide a method and system which has low treatment cost, is less affected by water quality fluctuations, has strong adaptability, and is suitable for treating eutrophic river and lake water bodies.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows: A method for treating eutrophic river and lake water, comprising setting a bypass and sequentially performing the following treatment steps: S1, extracting water from rivers and lakes to be treated for oxygen removal to obtain low-oxygen water; S2, introducing the hypoxic water body into a denitrification unit for autotrophic denitrification treatment to obtain a denitrified water body; S3, subjecting the denitrification water body to magnetic coagulation and phosphorus removal treatment to obtain denitrification and phosphorus removal water body.

[0007] In one embodiment of the present application, the processing method further satisfies one or more of the following conditions: The dissolved oxygen concentration of the hypoxic water body is below 1 mg / L; The residence time of the hypoxic water body in the denitrification unit for autotrophic denitrification treatment is 20 to 60 minutes, and the filtration rate is 1 to 8 m / h; The total nitrogen concentration of the denitrified water body is lower than 1.5 mg / L, and the nitrate nitrogen concentration is lower than 1.0 mg / L; The magnetic coagulation dephosphorization treatment comprises adding a dephosphorization agent, a magnetic medium and a coagulant to perform coagulation, flocculation and magnetic medium floc separation treatment; The total phosphorus concentration of the denitrification and phosphorus removal water body is lower than 0.1 mg / L, the SS concentration is lower than 5 mg / L, and the turbidity is lower than 1 NTU.

[0008] In one embodiment of the present application, one or more of the following processing steps are also included: S101, filtering the river and lake water to be treated, removing suspended matter and then performing the deoxidation treatment; S201, performing a nitrogen expulsion procedure on the denitrification unit, the nitrogen expulsion procedure comprising: stopping water inflow, pumping denitrification water to flow in reverse through the filter material area of ​​the denitrification unit, and resuming water inflow after nitrogen expulsion is completed; the frequency of the nitrogen expulsion procedure is 3 to 6 times a day, the nitrogen expulsion time is 1 to 2 minutes, and the nitrogen expulsion intensity is 4 to 6 L / (m 2 s); S202, the denitrification unit performs a backwashing procedure, which includes: stopping water inlet, and sequentially performing air washing, air-water washing, and water washing processes, and resuming water inlet after backwashing is completed; the backwashing procedure is performed once every 3 to 7 days, with an air washing time of 2 to 5 minutes, an air-water washing time of 5 to 8 minutes, and a water washing time of 5 to 10 minutes, and an air washing intensity of 14 to 30 L / (m 2 ·s), the water washing intensity is 4~6L / (m 2 s); S4, reoxygenating the denitrification and dephosphorization water body, and discharging the reoxygenated water body back into the river or lake water body.

[0009] In one embodiment of the present application, the reoxygenation treatment includes a combination of one or more treatments selected from the group consisting of waterfall, stirring, hydraulic mixing, and aeration, and the dissolved oxygen concentration of the reoxygenated water body is 6-8 mg / L.

[0010] In one embodiment of the present application, in step S1, the river and lake water to be treated is subjected to oxygen removal treatment to obtain a hypoxic water body, specifically including one of the following treatment methods; The river and lake water to be treated is introduced into the relative vacuum degree of -0.05~-0.09Mpa for deoxygenation treatment to obtain low-oxygen water; The river and lake water to be treated is mixed with the deoxidizer to react to achieve deoxidation treatment and obtain low-oxygen water.

[0011] In one embodiment of the present application, the deoxidizer is one or a combination of sodium sulfite and sodium thiosulfate, and the amount of the deoxidizer added is 23-90 mg / L based on the volume of river and lake water. Alternatively, the deoxidizer is ferrous sulfide, and the amount of the deoxidizer added is 6-30 mg / L based on the volume of river and lake water.

[0012] A eutrophic river and lake water treatment system comprises a filtration unit, an oxygen removal unit, a denitrification unit and a phosphorus removal unit arranged in sequence; The oxygen removal unit is used to reduce the dissolved oxygen concentration in river and lake water bodies; The denitrification unit is an autotrophic denitrification unit, which uses autotrophic denitrification microorganisms to perform biological denitrification; The phosphorus removal unit is a magnetic coagulation phosphorus removal unit.

[0013] In one embodiment of the present application, the oxygen removal unit includes one of the following forms: It comprises a pipeline mixing deoxidizer and a first deoxidizer dosing device, wherein the pipeline mixing deoxidizer is arranged before the water inlet of the denitrification unit, and the first deoxidizer dosing device is arranged to add deoxidizer to the pipeline mixing deoxidizer so that the water body can be deoxidized in the pipeline mixing deoxidizer; It comprises a chemical deoxidation tank and a second deoxidation agent dosing device, wherein the chemical deoxidation tank is arranged before the water inlet of the denitrification unit, and the second deoxidation agent dosing device is arranged to add deoxidation agent to the chemical deoxidation tank so that the water body can be deoxidized in the chemical deoxidation tank; It comprises a vacuum container and a vacuum pumping device. The vacuum container is arranged before the water inlet of the denitrification unit. The vacuum pumping device can vacuum the vacuum container to achieve oxygen removal of the water in the vacuum container.

[0014] In one embodiment of the present application, the filter unit comprises a coarse grid, a medium grid and a fine grid filter area arranged in sequence; and / or, The denitrification unit includes an autotrophic denitrification filter, a backwash device and a water storage tank; The autotrophic denitrification filter tank comprises a water inlet area, a filter material area and a water and gas distribution area arranged from top to bottom, the water inlet of the denitrification unit is located below the liquid surface of the water inlet area, the filter material area is filled with denitrification carrier fillers and autotrophic denitrifying microorganisms, and the water and gas distribution area is provided with a water outlet and a water and gas distributor; The backwash device comprises a backwash water pump and a backwash air pump, the backwash water pump is connected to the water and air distributor and the water storage tank, and the backwash air pump is connected to the water and air distributor; The water storage tank is connected to the water outlet of the denitrification unit, the inlet of the backwash water pump and the water inlet of the dephosphorization unit; and / or, The phosphorus removal unit includes a coagulation section, a flocculation section and a magnetic separation section which are arranged in sequence, and also includes a phosphorus removal agent dosing device, a magnetic medium dosing device, a coagulant dosing device and a magnetic medium recovery device; the phosphorus removal agent dosing device and the magnetic medium dosing device are connected to the coagulation section, and phosphorus removal agent and magnetic medium are added to the coagulation section. The front part of the coagulation section is a fast stirring zone, and the rear part is a slow stirring zone; the coagulant dosing device is connected to the flocculation section, and coagulant is added to the flocculation section; the magnetic medium recovery device is connected to the magnetic separation section and the coagulation section, and the flocs captured by the magnetic separation section are separated by magnetic media and recovered and added to the coagulation section.

[0015] In one embodiment of the present application, a reoxygenation unit is further included, and the reoxygenation unit is arranged after the phosphorus removal unit and before the water is discharged back to the river or lake; The reoxygenation unit comprises a plunge pool, a dissolved oxygen detector and a stirrer. The dissolved oxygen detector is arranged to detect the dissolved oxygen in the water body in the plunge pool, and the dissolved oxygen detector is associated with the stirrer.

[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. The eutrophic river and lake water treatment method and system of the present invention, by setting a bypass, adopts a combination of biological and physicochemical methods to achieve the removal of nitrogen and phosphorus pollutants in natural river and lake water bodies, and deoxygenates the water body before denitrification treatment to reduce the dissolved oxygen concentration of the water body, effectively solving the problem of oxygen enrichment in natural river and lake water bodies, avoiding the inhibition of the denitrification activity of the autotrophic denitrification denitrification unit by the oxygen-rich water body, ensuring that the autotrophic denitrification denitrification unit effectively denitrifies the water body, and the water body with low dissolved oxygen can further promote the efficiency of autotrophic denitrification and improve the treatment effect; in addition, after the denitrification treatment, magnetic coagulation and phosphorus removal treatment is carried out, so that the turbidity of the water body entering the magnetic coagulation and phosphorus removal treatment is reduced, which can greatly reduce the addition and use of chemical agents (phosphorus removal agents, coagulants), lower the operating cost, and reduce the risk of secondary pollution caused by chemical agent residues.

[0017] 2. Reoxygenate the water before discharging it back into rivers and lakes to increase and control the dissolved oxygen in the returned water, which can effectively reduce the impact on the returned water in rivers and lakes and reduce the risk of eutrophication.

[0018] 3. The eutrophic river and lake water treatment method and system of the present invention are suitable for the treatment of river and lake water with high dissolved oxygen and low carbon-nitrogen ratio. It has little disturbance to natural river and lake water, does not require additional addition of organic carbon source, uses less chemical agents, has low operating cost (the operating cost is reduced by more than 50% compared with heterotrophic denitrification, and there is no risk of COD exceeding the standard and carbon source penetration), and has a low risk of secondary pollution. The equipment is simple, occupies a small area, is easy to control, is less affected by fluctuations in water quality and quantity, and has guaranteed water quality. It can effectively remove total nitrogen, total phosphorus and SS (suspended solids) in water. It has strong applicability and is easy to promote and apply. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0020] Figure 1 The present invention is a flow chart of the method for treating eutrophic river and lake water bodies.

[0021] Figure 2 It is a schematic diagram of the process structure of the eutrophic river and lake water treatment system of the present invention. DETAILED DESCRIPTION

[0022] In the following, only some exemplary embodiments are briefly described. As those skilled in the art will appreciate, the described embodiments may be modified in various ways without departing from the spirit or scope of the present invention. Therefore, the drawings and descriptions are considered to be exemplary and non-restrictive in nature.

[0023] The embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0024] The embodiment of the present invention provides a method and system for treating eutrophic river and lake water bodies. The method and system are for setting up a bypass treatment system near the river and lake water bodies for treatment.

[0025] like Figure 1 As shown, the method for treating eutrophic river and lake water includes setting a treatment bypass near the natural river and lake water to be treated, and performing the following operation steps in sequence: S1, extracting water from rivers and lakes to be treated for deoxygenation treatment, reducing the dissolved oxygen concentration of the water from rivers and lakes to be treated, and obtaining low-oxygen water.

[0026] Specifically, optionally, a vacuum deoxygenation treatment method is used for deoxygenation treatment, specifically, the river and lake water to be treated is introduced into a container, and deoxygenation treatment is carried out under a relative vacuum degree of -0.05~-0.09MPa. Under the vacuum condition, the gases including oxygen dissolved in the water will be released, thereby reducing the dissolved oxygen concentration in the water, and the desired low-oxygen water can be obtained.

[0027] Optionally, deoxygenation treatment is carried out by chemical deoxygenation, specifically, the river and lake water to be treated is mixed with a deoxygenating agent for reaction, thereby achieving deoxygenation treatment and obtaining low-oxygen water.

[0028] Preferably, the deoxidizing agent includes one of sodium sulfite and sodium thiosulfate or a combination of the two. When sodium sulfite and / or sodium thiosulfate are used as deoxidizing agents, the amount of deoxidizing agent added is controlled to be 23-90 mg / L based on the volume of the river and lake water being treated, so as to obtain the desired low-oxygen water.

[0029] Optionally, the deoxidizing agent may be ferrous sulfide. When ferrous sulfide is used as the deoxidizing agent, the amount of ferrous sulfide added is controlled to be 6-30 mg / L based on the volume of the river and lake water being treated, and the desired low-oxygen water body can be obtained.

[0030] Preferably, the dissolved oxygen concentration of the obtained hypoxic water body is controlled to be below 1 mg / L, which can provide a good anaerobic basis for subsequent autotrophic denitrification treatment.

[0031] S2, introducing the hypoxic water body obtained in step S1 into a denitrification unit for autotrophic denitrification treatment by autotrophic denitrifying microorganisms to remove total nitrogen and nitrate nitrogen in the water body, and obtaining denitrified water body with low nitrogen concentration after denitrification treatment.

[0032] It is preferred that the denitrification unit adopts the form of an autotrophic denitrification filter tank. The residence time of the hypoxic water body in the denitrification unit for autotrophic denitrification treatment is controlled to be 20-60 minutes, and the filtration rate is controlled to be 1-8 m / h, so that the desired denitrified water body can be obtained. The total nitrogen concentration of the denitrified water body obtained is less than 1.5 mg / L, and the nitrate nitrogen concentration is less than 1.0 mg / L.

[0033] S3, subjecting the denitrified water body obtained in step S2 to magnetic coagulation and phosphorus removal treatment to remove phosphate pollutants in the water body, and further obtaining a denitrified and phosphorus removed water body with a low total phosphorus concentration.

[0034] Preferably, the magnetic coagulation phosphorus removal treatment includes adding a phosphorus removal agent, a magnetic medium and a coagulant to perform coagulation and flocculation treatment, and after the flocculation treatment, performing a magnetic medium floc separation treatment to obtain a denitrification and dephosphorization water body with phosphate pollutants removed.

[0035] Specifically, the dephosphorization agent and magnetic medium are first added for stirring treatment, and preferably two-stage stirring is adopted, namely, rapid stirring first and slow stirring second, which can be conducive to sufficient coagulation, promote the formation of flocs, enhance the phosphorus removal effect and ensure uniform magnetization of flocs; then, a coagulant is added, and differential stirring is adopted to better promote the further growth of flocs, which is conducive to the subsequent floc sedimentation and magnetic separation; the magnetic medium floc separation treatment adopts a super magnetic separator to adsorb the flocs containing the magnetic medium onto the magnetic plate, so as to separate the flocs from the water body and obtain the denitrification and dephosphorization water body; the flocs containing the magnetic medium adsorbed by the super magnetic separator are transported to the magnetic medium recovery processing device by hanging down through the scraper bar, so as to separate the magnetic medium from the flocs and recover the magnetic medium.

[0036] Among them, the phosphorus removal agent includes one or more combinations of polyaluminum chloride (PAC), polyaluminum ferric chloride (PAFC), polyaluminum chloride (PAC), polyferric chloride (PFC), polyferric sulfate (PFS), polyferrous iron, polyferric chloride sulfate (PFCS), polyaluminum ferric chloride sulfate (PAFCS), and polyaluminum sulfate (PFAS).

[0037] The magnetic medium is magnetic powder.

[0038] Coagulant aids include polyacrylamide (PAM) and / or diatomaceous earth.

[0039] The total phosphorus concentration of the denitrification and phosphorus removal water obtained after control treatment is less than 0.1mg / L, the SS (suspended solids) concentration is less than 5mg / L, and the turbidity is less than 1NTU. The denitrification and phosphorus removal water is discharged back to natural rivers and lakes, which can effectively avoid nitrogen and phosphorus pollution and eutrophication of water bodies.

[0040] In one embodiment, the method further includes step S101, filtering the river and lake water to be treated to remove large suspended solids in the water, and then performing the deoxidation treatment in step S1. Performing the filtering treatment first is conducive to the normal and efficient operation of the subsequent denitrification unit, and prolonging the service life of the denitrification unit, especially the autotrophic denitrification filter.

[0041] The step S201 is also included, in which the denitrification unit is periodically subjected to a nitrogen removal procedure, wherein the nitrogen removal procedure includes: stopping water inlet, pumping denitrification water into the filter material area of ​​the denitrification unit through a backwash water pump, and subjecting the denitrification carrier filler in the filter material area to nitrogen removal treatment to remove the gas (mainly nitrogen) attached to the surface of the denitrification carrier filler, and resuming water inlet after the nitrogen removal is completed to continue the denitrification treatment.

[0042] Preferably, the nitrogen expulsion program of step S201 is started 3 to 6 times a day; the nitrogen expulsion time is preferably 1 to 2 minutes each time, and the nitrogen expulsion intensity is 4 to 6 L / (m 2 ·s). It can effectively remove the gas attached to the denitrification carrier filler, ensuring that the denitrification unit can carry out denitrification treatment efficiently and stably.

[0043] It also includes step S202, which periodically performs a backwash procedure on the denitrification unit. The backwash procedure includes: stopping water inlet, pumping air and / or denitrification water into the unit through a backwash air pump and a backwash water pump, and sequentially performing air washing, air-water washing, and water washing processes. After the backwash is completed, water inlet is resumed to continue the denitrification treatment.

[0044] Preferably, the backwashing procedure in step S202 is started once every 3 to 7 days.

[0045] The time of the air washing process in each backwashing procedure is controlled to be 2-5 minutes; the time of the air-water washing process is controlled to be 5-8 minutes; the time of the water washing process is controlled to be 5-10 minutes; the preferred air washing intensity is 14-30L / (m 2 ·s), the water washing intensity is 4~6L / (m 2 ·s).

[0046] Preferably, the method further includes step S4, in which the denitrification and dephosphorization water obtained by the step S3 is further subjected to reoxygenation treatment to increase the dissolved oxygen concentration of the denitrification and dephosphorization water, obtain reoxygenated water with a suitable dissolved oxygen concentration, and then discharge the reoxygenated water back into natural river and lake water bodies.

[0047] The reoxygenation treatment includes a combination of one or more treatment methods such as waterfall, stirring, hydraulic mixing, and aeration. Preferably, the dissolved oxygen concentration of the reoxygenated water body is controlled to be 6-8 mg / L. The denitrification and dephosphorization water body is reoxygenated and then discharged back to the natural river and lake water body, which can effectively avoid the problem of hypoxia in natural water bodies affecting aquatic biodiversity and reduce the risk of eutrophication.

[0048] Compared with traditional physical and chemical treatment methods, this eutrophic river and lake water treatment method causes less disturbance to natural water bodies and has a low risk of secondary pollution. It can simultaneously, quickly and effectively remove SS, total nitrogen and total phosphorus. It avoids the addition of carbon sources, has low operating costs and no risk of carbon source penetration. It can also be precisely regulated according to the influent water quality, with simple control and operation, and stable and reliable treated water quality.

[0049] Based on the same invention purpose and concept, the present invention also provides a eutrophic river and lake water treatment system, which is configured as a bypass system and is suitable for using the above-mentioned treatment method to perform denitrification and phosphorus removal on eutrophic river and lake water.

[0050] like Figure 2 As shown, the eutrophic river and lake water treatment system includes a filtration unit, an oxygen removal unit, a denitrification unit and a phosphorus removal unit which are arranged in sequence.

[0051] Among them, the deoxygenation unit is used to reduce the dissolved oxygen concentration in river and lake water bodies.

[0052] The denitrification unit is an autotrophic denitrification unit, which is inoculated with autotrophic denitrification microorganisms, and biological denitrification of the water body is carried out by the autotrophic denitrification microorganisms.

[0053] The phosphorus removal unit is a magnetic coagulation phosphorus removal unit, which removes phosphate pollutants by combining magnetic media with coagulation flocs, thereby reducing the total phosphorus concentration in the water.

[0054] The system combines biological and physicochemical methods. It deoxygenates the water before entering the denitrification unit for denitrification treatment to reduce the dissolved oxygen concentration in the water, effectively solving the problem of oxygen enrichment in natural river and lake waters and avoiding the inhibition of the denitrification activity of the autotrophic denitrification denitrification unit by oxygen-rich waters. This ensures that the autotrophic denitrification denitrification unit effectively denitrifies the water, and the water with low dissolved oxygen can further promote the efficiency of autotrophic denitrification and improve the treatment effect. A magnetic coagulation and phosphorus removal unit is set after the denitrification unit, that is, magnetic coagulation and phosphorus removal is carried out after the denitrification treatment, so that the turbidity of the water entering the magnetic coagulation and phosphorus removal unit is reduced (can be reduced to about 5NTU), which can greatly reduce the addition and use of chemical agents (phosphorus removal agents, coagulants), lower operating costs, and reduce the risk of secondary pollution caused by chemical agent residues.

[0055] In one embodiment, the deoxidation unit includes a pipeline mixing deoxidizer and a first deoxidizer dosing device. The pipeline mixing deoxidizer is arranged before the water inlet of the denitrification unit or on the water inlet pipeline; the first deoxidizer dosing device is connected to the pipeline mixing deoxidizer and is arranged to add deoxidizer to the pipeline mixing deoxidizer so that the water body is deoxidized in the pipeline mixing deoxidizer, and the low-oxygen water body is obtained and then discharged into the denitrification unit.

[0056] Specifically, the water filtered by the filtration unit enters the pipeline mixing deoxidizer, and at the same time, the first deoxidizer dosing device dissolves the deoxidizer (such as sodium sulfite, sodium thiosulfate, etc.) and adds it to the pipeline mixing deoxidizer. The water and the deoxidizer are fully mixed hydraulically in the pipeline mixing deoxidizer to achieve a deoxidation reaction, and the low-oxygen water is obtained and enters the subsequent denitrification unit for autotrophic denitrification treatment.

[0057] In another embodiment, the deoxidation unit includes a chemical deoxidation tank and a second deoxidation agent dosing device. The chemical deoxidation tank is arranged before the water inlet of the denitrification unit and between the filtration unit and the denitrification unit; the second deoxidation agent dosing device is connected to the chemical deoxidation tank and is arranged to add deoxidation agent to the chemical deoxidation tank so that the water body is deoxidized in the chemical deoxidation tank, and the low-oxygen water body is obtained and then discharged to the denitrification unit.

[0058] Specifically, the water filtered by the filtration unit enters the chemical deoxidation tank, and the deoxidant (such as sodium sulfite, sodium thiosulfate, ferrous sulfide, etc.) is dissolved through the second deoxidant dosing device and then put into the chemical deoxidation tank or directly put into the chemical deoxidation tank. The water reacts with the deoxidant in the chemical deoxidation tank to achieve deoxidation, and the low-oxygen water is obtained and then discharged to the denitrification unit.

[0059] In the third embodiment, the deoxidation unit includes a vacuum container and a vacuum pump. The vacuum container, such as a vacuum deoxidizer, is arranged before the water inlet of the denitrification unit, that is, the vacuum container is arranged between the filtration unit and the denitrification unit; the vacuum pump (such as a vacuum pump) is connected to the vacuum container, and can evacuate the vacuum container to deoxidize the water in the vacuum container. When this vacuum deoxidation method is adopted, an inlet valve / inlet pump is also provided at the water inlet end of the vacuum container to introduce the water into the vacuum container; at the same time, a water outlet pump is also provided between the vacuum container and the denitrification unit to draw out the water in the vacuum container and discharge it to the denitrification unit.

[0060] Specifically, during operation, the vacuum device is first turned on, and the vacuum degree is designed according to the expected concentration of dissolved oxygen to be removed. Preferably, the relative vacuum degree is set to -0.05MPa~-0.09MPa. When the relative vacuum degree in the vacuum container reaches the set value, the water inlet valve / water inlet pump is opened to introduce the outlet water of the filtration unit into the vacuum container, and ensure that the liquid level and relative vacuum degree in the vacuum container are within the set range. Under the vacuum environment, the gases including oxygen dissolved in the water body will be released, thereby reducing the dissolved oxygen concentration in the water; the obtained low-oxygen water body is discharged through the outlet pump to the subsequent denitrification unit for denitrification treatment.

[0061] The filtration unit is arranged at the front end of the system, and preferably includes a water pump, a coarse grid, a medium grid and a fine grid filtration area arranged in sequence. The water body is filtered through the coarse grid, the medium grid and the fine grid filtration area in sequence, which can well achieve the removal of large volume suspended solids, ensure the normal and efficient subsequent treatment, and increase the service life of the denitrification unit.

[0062] In one embodiment, the denitrification unit includes an autotrophic denitrification filter, a backwash device, a water storage tank, etc. The autotrophic denitrification filter includes an inlet area, a filter area, and a water and gas distribution area arranged from top to bottom. The water inlet of the denitrification unit is located below the liquid surface of the water inlet area, and the water inlet is immersed below the liquid surface to avoid the increase of dissolved oxygen in the water body caused by the fall. The filter area is filled with denitrification carrier fillers and inoculated with autotrophic denitrifying microorganisms, which are used to filter the water body and realize autotrophic denitrification. The water and gas distribution area is provided with a water outlet and a water and gas distributor, and the water outlet is connected to the dephosphorization unit for discharging the denitrified water body after denitrification treatment; the water and gas distributor is connected to the backwash device for dispersing the backwash water / gas during backwashing / nitrogen expulsion. Preferably, the height of the water inlet area is 1~1.5m, the height of the filter area is 2~3m, and the height of the water and gas distribution area is 0.5~1.0m, which can ensure continuous and stable filtration and denitrification treatment.

[0063] The backwash device includes a backwash water pump and a backwash air pump. The outlet end of the backwash water pump is connected to a water and air distributor, and the inlet end is connected to a water storage tank. The denitrification water body is used to backwash and drive nitrogen from the autotrophic denitrification filter. The outlet end of the backwash air pump is connected to a water and air distributor to pump compressed gas into the autotrophic denitrification filter for air washing.

[0064] The water storage tank is connected to the outlet of the denitrification unit, the inlet of the backwash water pump and the water inlet of the phosphorus removal unit. The water storage tank is set between the autotrophic denitrification filter and the phosphorus removal unit to ensure the continuous and stable operation of the system. At the same time, the denitrification water body can be used for backwashing and nitrogen expulsion of the autotrophic denitrification filter, saving operating costs and water.

[0065] In one embodiment, the phosphorus removal unit includes a coagulation section, a flocculation section and a magnetic separation section which are arranged in sequence, and also includes a phosphorus removal agent dosing device, a magnetic medium dosing device, a coagulant dosing device and a magnetic medium recovery device.

[0066] Among them, the phosphorus removal agent dosing device and the magnetic medium dosing device are connected to the coagulation section, and are used to automatically add the phosphorus removal agent and the magnetic medium to the coagulation section respectively; the coagulation section is provided with two-stage stirring zones, the front part is provided with a fast stirring zone, and the rear part is provided with a slow stirring zone, the phosphorus removal agent and the magnetic medium are quickly dispersed and mixed in the fast stirring zone, which is conducive to the formation of flocs and uniform contact with the magnetic medium, and then enter the slow stirring zone, which is conducive to the further formation of the flocs and the weight increase and magnetization, which can effectively improve the phosphorus removal effect. The coagulant dosing device is connected to the flocculation section, and is used to add the coagulant to the flocculation section. The magnetic medium recovery device is provided to connect the magnetic separation section and the coagulation section, and the flocs containing phosphorus and magnetic medium captured by the magnetic separation section are separated and recovered by magnetic medium, and the recovered magnetic medium is added to the coagulation section for recycling.

[0067] Specifically, the denitrified water stored in the water storage tank enters the coagulation section, and the dephosphorization agent dosing device and the magnetic medium dosing device respectively add the dephosphorization agent and the magnetic medium into the rapid stirring zone, and the dephosphorization agent and the magnetic medium react with the phosphate pollutants in the denitrified water and flow to the slow stirring zone to gradually form magnetic flocs; then it enters the flocculation section, reacts with the coagulant added by the coagulant dosing device, and forms phosphorus-containing and magnetic medium flocs of larger size that are easier to capture; then it enters the magnetic separation section, and the flocs are captured by magnetic separation equipment (such as a super magnetic separator), and the captured phosphorus-containing and magnetic medium flocs enter the magnetic medium recovery device to separate the magnetic medium from the flocs, and the separated magnetic medium can be recovered and added to the coagulation section for recycling, and the separated phosphorus-containing sludge is discharged, thereby realizing the phosphorus removal treatment of the water body and obtaining denitrified and dephosphorized water.

[0068] In one embodiment, it also includes a reoxygenation unit, which is arranged after the phosphorus removal unit and before being discharged back to the river and lake water body, and is used to increase the dissolved oxygen concentration of the discharged denitrification and dephosphorization water body.

[0069] The reoxygenation unit may include a combination of one or more of a waterfall pool, a stirring pool, a hydraulic mixer, and an aeration device. The dissolved oxygen in the denitrification and dephosphorization water body is increased by dropping from a height, stirring, hydraulic mixing, aeration, etc., so as to reduce the impact on the river and lake water bodies and reduce the risk of eutrophication.

[0070] Preferably, the reoxygenation unit includes a plunge pool, a dissolved oxygen detector and an agitator. The dissolved oxygen detector is arranged to detect the dissolved oxygen in the water body in the plunge pool, and the dissolved oxygen detector is associated with the agitator, and the agitator can be controlled to run or stop according to the dissolved oxygen concentration value of the water body. When the dissolved oxygen concentration of the water body in the plunge pool is high and meets the discharge requirements, the agitator stops running; when the dissolved oxygen concentration of the water body in the plunge pool is low and is lower than the lower limit of the discharge requirements, the agitator starts to stir to further increase the dissolved oxygen concentration.

[0071] The eutrophic river and lake water treatment system also includes a control unit, which is connected to the filtration unit, the oxygen removal unit, the nitrogen removal unit, the phosphorus removal unit and the reoxygenation unit to achieve automated coordinated control of the system.

[0072] In summary, the eutrophic river and lake water treatment method and system of the present invention, by setting up a bypass, adopts a combination of biological and physicochemical methods to achieve the removal of nitrogen and phosphorus pollutants in natural river and lake water bodies, and deoxygenates the water body before denitrification treatment to reduce the dissolved oxygen concentration in the water body, effectively solving the problem of oxygen enrichment in natural river and lake water bodies, avoiding the inhibition of the denitrification activity of the autotrophic denitrification denitrification unit by the oxygen-rich water body, ensuring that the autotrophic denitrification denitrification unit effectively denitrifies the water body, and the water body with low dissolved oxygen can further promote the efficiency of autotrophic denitrification and improve the treatment effect; in addition, after the denitrification treatment, magnetic coagulation and phosphorus removal treatment is carried out, so that the turbidity of the water body entering the magnetic coagulation and phosphorus removal treatment is reduced, which can greatly reduce the addition and use of chemical agents (phosphorus removal agents, coagulants), lower the operating cost, and reduce the risk of secondary pollution caused by chemical agent residues.

[0073] Reoxygenating the water before discharging it back into rivers and lakes can improve and control the dissolved oxygen concentration of the returned water, which can effectively reduce the impact on the returned water in rivers and lakes, avoid the problem of hypoxia in natural water bodies affecting aquatic biodiversity, and reduce the risk of eutrophication.

[0074] The eutrophic river and lake water treatment method and system of the present invention are suitable for treating river and lake water with high dissolved oxygen and low carbon-nitrogen ratio. It has little disturbance to natural river and lake water, does not require additional addition of organic carbon source, uses less chemical agents, has low operating cost (the operating cost is reduced by more than 50% compared with heterotrophic denitrification, and there is no risk of COD exceeding the standard and carbon source penetration), and has a low risk of secondary pollution. The equipment is simple, occupies a small area, is easy to control, is less affected by fluctuations in water quality and water quantity, and the quality of treated water is guaranteed. It can effectively remove total nitrogen, total phosphorus and SS (suspended solids) in water. It has strong applicability and is easy to promote and apply.

[0075] When the total nitrogen in the inlet water is 2~15mg / L, the total phosphorus is 0.1~1.0m / L, and the SS is 10~200mg / L, the treatment method and treatment system of the present application can be used to reduce the total nitrogen concentration of the effluent to below 1.5mg / L, the nitrate nitrogen concentration to below 1.0mg / L, the total phosphorus concentration to below 0.1mg / L, the SS concentration to below 5mg / L, and the turbidity to below 1NTU, thereby obtaining effluent that meets the treatment requirements.

Claims

1. A method for treating eutrophic river and lake water, characterized in that: Including setting up bypass, perform the following processing steps in sequence: S1, extracting water from rivers and lakes to be treated for oxygen removal to obtain low-oxygen water; S2, introducing the hypoxic water body into a denitrification unit for autotrophic denitrification treatment to obtain a denitrified water body; S3, subjecting the denitrification water body to magnetic coagulation and phosphorus removal treatment to obtain denitrification and phosphorus removal water body.

2. The method for treating eutrophic river and lake water according to claim 1, characterized in that: The processing method also meets one or more of the following conditions: The dissolved oxygen concentration of the hypoxic water body is below 1 mg / L; The residence time of the hypoxic water body in the denitrification unit for autotrophic denitrification treatment is 20 to 60 minutes, and the filtration rate is 1 to 8 m / h; The total nitrogen concentration of the denitrified water body is lower than 1.5 mg / L, and the nitrate nitrogen concentration is lower than 1.0 mg / L; The magnetic coagulation dephosphorization treatment comprises adding a dephosphorization agent, a magnetic medium and a coagulant to perform coagulation, flocculation and magnetic medium floc separation treatment; The total phosphorus concentration of the denitrification and phosphorus removal water body is lower than 0.1 mg / L, the SS concentration is lower than 5 mg / L, and the turbidity is lower than 1 NTU.

3. The method for treating eutrophic river and lake water according to claim 1, characterized in that: It also includes one or more of the following processing steps: S101, filtering the river and lake water to be treated, removing suspended matter and then performing the deoxidation treatment; S201, performing a nitrogen expulsion procedure on the denitrification unit, the nitrogen expulsion procedure comprising: stopping water inflow, pumping denitrification water to flow in reverse through the filter material area of ​​the denitrification unit, and resuming water inflow after nitrogen expulsion is completed; the frequency of the nitrogen expulsion procedure is 3 to 6 times a day, the nitrogen expulsion time is 1 to 2 minutes, and the nitrogen expulsion intensity is 4 to 6 L / (m 2 s); S202, the denitrification unit performs a backwashing procedure, which includes: stopping water inlet, and sequentially performing air washing, air-water washing, and water washing processes, and resuming water inlet after backwashing is completed; the backwashing procedure is performed once every 3 to 7 days, with an air washing time of 2 to 5 minutes, an air-water washing time of 5 to 8 minutes, and a water washing time of 5 to 10 minutes, and an air washing intensity of 14 to 30 L / (m 2 ·s), the water washing intensity is 4~6L / (m 2 s); S4, reoxygenating the denitrification and dephosphorization water body, and discharging the reoxygenated water body back into the river or lake water body.

4. The method for treating eutrophic river and lake water according to claim 3, characterized in that: The reoxygenation treatment includes a combination of one or more treatments selected from the group consisting of waterfall, stirring, hydraulic mixing, and aeration. The dissolved oxygen concentration of the reoxygenated water body is 6-8 mg / L.

5. The method for treating eutrophic river and lake water according to claim 1, characterized in that: In step S1, the river and lake water to be treated is subjected to oxygen removal treatment to obtain hypoxic water, which specifically includes one of the following treatment methods; The river and lake water to be treated is introduced into the relative vacuum degree of -0.05~-0.09MPa for deoxygenation treatment to obtain low-oxygen water; The river and lake water to be treated is mixed with the deoxidizer to react to achieve deoxidation treatment and obtain low-oxygen water.

6. The method for treating eutrophic river and lake water according to claim 5, characterized in that: The deoxidizer is one or a combination of sodium sulfite and sodium thiosulfate. The amount of the deoxidizer added is 23-90 mg / L based on the volume of the river or lake water. Alternatively, the deoxidizer is ferrous sulfide, and the amount of the deoxidizer added is 6-30 mg / L based on the volume of river and lake water.

7. A eutrophic river and lake water treatment system, characterized in that: It includes a filtration unit, an oxygen removal unit, a nitrogen removal unit and a phosphorus removal unit which are arranged in sequence; The oxygen removal unit is used to reduce the dissolved oxygen concentration in river and lake water bodies; The denitrification unit is an autotrophic denitrification unit, which uses autotrophic denitrification microorganisms to perform biological denitrification; The phosphorus removal unit is a magnetic coagulation phosphorus removal unit.

8. The eutrophic river and lake water treatment system according to claim 7, characterized in that: The deoxidation unit comprises one of the following forms: It comprises a pipeline mixing deoxidizer and a first deoxidizer dosing device, wherein the pipeline mixing deoxidizer is arranged before the water inlet of the denitrification unit, and the first deoxidizer dosing device is arranged to add deoxidizer to the pipeline mixing deoxidizer so that the water body can be deoxidized in the pipeline mixing deoxidizer; It comprises a chemical deoxidation tank and a second deoxidation agent dosing device, wherein the chemical deoxidation tank is arranged before the water inlet of the denitrification unit, and the second deoxidation agent dosing device is arranged to add deoxidation agent to the chemical deoxidation tank so that the water body can be deoxidized in the chemical deoxidation tank; It comprises a vacuum container and a vacuum pumping device. The vacuum container is arranged before the water inlet of the denitrification unit. The vacuum pumping device can vacuum the vacuum container to achieve oxygen removal of the water in the vacuum container.

9. The eutrophic river and lake water treatment system according to claim 7, characterized in that: The filter unit comprises a coarse grid, a medium grid and a fine grid filter area arranged in sequence; and / or, The denitrification unit includes an autotrophic denitrification filter, a backwash device and a water storage tank; The autotrophic denitrification filter tank comprises a water inlet area, a filter material area and a water and gas distribution area arranged from top to bottom, the water inlet of the denitrification unit is located below the liquid surface of the water inlet area, the filter material area is filled with denitrification carrier fillers and autotrophic denitrifying microorganisms, and the water and gas distribution area is provided with a water outlet and a water and gas distributor; The backwash device comprises a backwash water pump and a backwash air pump, the backwash water pump is connected to the water and air distributor and the water storage tank, and the backwash air pump is connected to the water and air distributor; The water storage tank is connected to the water outlet of the denitrification unit, the inlet of the backwash water pump and the water inlet of the dephosphorization unit; and / or, The phosphorus removal unit includes a coagulation section, a flocculation section and a magnetic separation section which are arranged in sequence, and also includes a phosphorus removal agent dosing device, a magnetic medium dosing device, a coagulant dosing device and a magnetic medium recovery device; the phosphorus removal agent dosing device and the magnetic medium dosing device are connected to the coagulation section, and phosphorus removal agent and magnetic medium are added to the coagulation section. The front part of the coagulation section is a fast stirring zone, and the rear part is a slow stirring zone; the coagulant dosing device is connected to the flocculation section, and coagulant is added to the flocculation section; the magnetic medium recovery device is connected to the magnetic separation section and the coagulation section, and the flocs captured by the magnetic separation section are separated by magnetic media and recovered and added to the coagulation section.

10. The eutrophic river and lake water treatment system according to claim 7, characterized in that: It also includes a reoxygenation unit, which is arranged after the phosphorus removal unit and before the water is discharged back to the river or lake; The reoxygenation unit comprises a plunge pool, a dissolved oxygen detector and a stirrer. The dissolved oxygen detector is arranged to detect the dissolved oxygen in the water body in the plunge pool, and the dissolved oxygen detector is associated with the stirrer.

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