An enhanced nitrogen removal treatment method for tail water based on constructed wetland and a constructed wetland system

Abstract

The present invention relates to a method for enhanced nitrogen removal from tail water based on a constructed wetland and a constructed wetland system. The method for enhanced nitrogen removal from tail water based on a constructed wetland includes: arranging a denitrification nitrogen removal area and an aerobic carbon reduction area between the water inlet area and the water outlet area of the constructed wetland, and the denitrification nitrogen removal area is provided with a mixed filler layer; diluting the anoxic sludge and introducing it into the water inlet area, the denitrification nitrogen removal area, the aerobic carbon reduction area and the water outlet area of the constructed wetland to achieve the first-stage biofilm formation treatment; introducing the tail water into the water inlet area, the denitrification nitrogen removal area, the aerobic carbon reduction area and the water outlet area of the constructed wetland to achieve the second-stage biofilm formation treatment; introducing the tail water into the water inlet area, the denitrification nitrogen removal area, the aerobic carbon reduction area and the water outlet area of the constructed wetland until the total nitrogen removal rate in the tail water reaches the standard and then discharging it. The present invention also provides a constructed wetland system. The present invention solves the problems of low nitrogen removal efficiency of the traditional constructed wetland for the tail water of urban sewage treatment plants and still relatively high total nitrogen concentration in the effluent water quality.

Description

Technical Field

[0001] The present invention relates to the technical field of sewage treatment, and particularly relates to a method for enhanced nitrogen removal from tail water based on constructed wetland and a constructed wetland system. Background Art

[0002] Tail water generally has the characteristic of a low C / N ratio, and nitrogen is mainly in the form of nitrate nitrogen. If directly discharged without effective treatment, it will lead to eutrophication of the receiving water body and cause serious impacts on the environment.

[0003] Currently, the advanced treatment of the tail water from urban sewage treatment plants, especially the advanced nitrogen removal treatment, has become a research hotspot in the environmental protection field. Traditional advanced nitrogen removal treatment methods include chemical methods, physical methods, biochemical methods, and natural ecological technologies such as constructed wetlands. Among them, the constructed wetland technology has attracted much attention due to its advantages such as low cost, environmental friendliness, and significant ecological effects. However, for the tail water of urban sewage treatment plants with a low C / N ratio, the denitrifying microorganisms in traditional subsurface flow constructed wetlands are mainly heterotrophic bacteria, and these microorganisms require additional carbon sources as electron donors during the denitrification process. Therefore, in practical applications, in order to improve the denitrification efficiency, it is often necessary to add carbon sources to the wetland system, which not only increases the operating cost but also brings inconvenience in management. At the same time, the organic matter released by the added carbon source may cause an increase in the chemical oxygen demand (COD) of the effluent and affect the effluent quality.

[0004] In recent years, autotrophic denitrification processes represented by sulfur autotrophic denitrification have attracted much attention due to their high denitrification efficiency. Although the sulfur autotrophic denitrification process has a good removal effect on nitrate nitrogen, the construction cost of the constructed wetland is relatively high due to the need to add sulfur sources such as sulfur, and the SO4 2- content in the effluent quality is relatively high, which poses a challenge to the control of the effluent quality. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a method for enhanced nitrogen removal from tail water based on constructed wetland and a constructed wetland system to solve the problems of low denitrification efficiency of traditional constructed wetlands for the tail water of urban sewage treatment plants, still relatively high total nitrogen concentration in the effluent quality, as well as the problems of difficult management and high operating cost.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0007] A method for enhanced nitrogen removal from tail water based on constructed wetland includes the following steps:

[0008] S1. A denitrification and nitrogen removal zone and an aerobic carbon reduction zone are arranged between the influent zone and the effluent zone of the constructed wetland. The denitrification and nitrogen removal zone is at least provided with a mixed filler layer, and the mixed filler layer at least comprises a plant slow-release carbon source. The constructed wetland is a folded subsurface flow constructed wetland.

[0009] S2. Dilute the anoxic sludge and introduce it into the influent zone, denitrification and nitrogen removal zone, aerobic carbon reduction zone and effluent zone of the constructed wetland, and maintain the hydraulic retention time greater than or equal to the first time under the first temperature condition, and then discharge it to achieve the first-stage biofilm formation treatment.

[0010] S3. Introduce the tail water into the influent zone, denitrification and nitrogen removal zone, aerobic carbon reduction zone and effluent zone of the constructed wetland, and maintain the hydraulic retention time greater than or equal to the second time under the second temperature condition to achieve the second-stage biofilm formation treatment.

[0011] S4. Introduce the tail water into the influent zone, denitrification and nitrogen removal zone, aerobic carbon reduction zone and effluent zone of the constructed wetland, and maintain the hydraulic retention time within the third time range under the third temperature condition, so that the tail water is treated by a hybrid nutrient denitrification system under the synergistic action of heterotrophic denitrification and sulfur autotrophic denitrification until the total nitrogen removal rate in the tail water reaches the standard and then is discharged.

[0012] According to the above technical means, by filling a plant slow-release carbon source in the denitrification and nitrogen removal zone of the constructed wetland and using the sulfate in the tail water of the sewage treatment plant at the same time, a hybrid nutrient denitrification system that combines heterotrophic denitrification and sulfur autotrophic denitrification is jointly driven, ensuring that the treatment method has high nitrogen removal efficiency and greenhouse gas emission reduction effect. The treatment method of the present invention combines the hybrid nutrient denitrification technology with the folded subsurface flow constructed wetland, effectively strengthens the deep nitrogen removal process of the tail water of sewage treatment plants with a low C / N ratio, and has the characteristics of synergistic reduction of pollution and carbon, and has the advantages of high nitrogen removal efficiency, less carbon emission, simple management and low operation cost, so that the effluent pollutants including TN and COD can reach the Class IV standard of surface water.

[0013] The enhanced nitrogen removal treatment method for tail water based on the constructed wetland of the present invention is mainly aimed at the deep removal of nitrogen in the tail water of urban sewage treatment plants, especially for the removal of nitrate nitrogen (NO3 - -N) and total nitrogen (TN) in the water quality. The system is divided into a hybrid nutrient denitrification and nitrogen removal zone and an aerobic carbon oxidation zone. Microorganisms in the hybrid nutrient denitrification and nitrogen removal zone carry out heterotrophic denitrification and sulfur autotrophic denitrification respectively, using the plant slow-release carbon source and the sulfate in the tail water as electron donors and nitrate nitrogen as the electron acceptor to achieve deep nitrogen removal of the tail water of the sewage treatment plant. Microorganisms in the aerobic carbon oxidation zone degrade the remaining organic matter (COD).

[0014] Preferably, in the step S3, the denitrification and nitrogen removal zone at least contains sulfate-reducing bacteria, heterotrophic denitrifying bacteria, and autotrophic denitrifying bacteria including Thiobacillus denitrificans;

[0015] Microorganisms such as sulfate-reducing bacteria in the biofilm utilize the slow-release carbon source of plants for chemoheterotrophy to reduce sulfate in the tail water to sulfide; sulfide or elemental sulfur is utilized by chemolithoautotrophic microorganisms such as Thiobacillus denitrificans as an electron donor to reduce nitrate in the tail water to nitrogen; the autotrophic denitrifying bacteria including Thiobacillus denitrificans control the pH of the effluent through the neutralization of the acid generated by autotrophic denitrification and the alkalinity generated by heterotrophic denitrification.

[0016] Among them, the sulfate-reducing bacteria, Thiobacillus denitrificans, and autotrophic denitrifying bacteria are obtained by enrichment growth during the biofilm formation process in the second stage.

[0017] Preferably, the step S2 is carried out more than twice to ensure the growth of stable heterotrophic microorganisms in the biofilm in the denitrification and nitrogen removal zone.

[0018] Preferably, the first temperature is 10°C to 30°C.

[0019] Preferably, the first time is 72 h.

[0020] Preferably, the second temperature is 20°C to 30°C.

[0021] Preferably, the second time is 48 h.

[0022] Preferably, the third temperature is 10°C to 35°C.

[0023] Preferably, the third time is 2 d to 3 d.

[0024] Preferably, in the step S2, the anoxic sludge is the sludge from the anoxic tank of a municipal wastewater treatment plant, and the anoxic sludge is diluted to a concentration < 1 g / L.

[0025] Preferably, in the step S3, the tail water is the secondary effluent or reclaimed water from a municipal wastewater treatment plant, the C / N ratio of the tail water ≤ 3, and the mass concentration of nitrate nitrogen (NO3 - -N) in the tail water ≤ 16 mg / L.

[0026] The present invention also provides a constructed wetland system for implementing the tail water enhanced denitrification treatment method as described in the present invention, which at least includes an inlet area, a denitrification and nitrogen removal area, an aerobic carbon reduction area, and an outlet area arranged in sequence. The adjacent areas between the inlet area, the denitrification and nitrogen removal area (A-section reaction area), the aerobic carbon reduction area (O-section reaction area), and the outlet area are separated by partition boards, and all the partition boards are arranged in a vertically offset manner to form a folded horizontal subsurface flow constructed wetland bed;

[0027] The denitrification and nitrogen removal zone includes, from bottom to top, a supporting layer, a first mixed filler layer, and a plant planting layer arranged in sequence.

[0028] According to the above technical means, the constructed wetland system of the present invention, without changing the structure of the horizontal subsurface flow constructed wetland, improves the hydraulic characteristics of the wetland system by installing non-equidistant partition plates inside the bed body, and constructs an A / O denitrification treatment process with different volumes and functions. It not only prolongs the hydraulic retention time of the A-section reaction zone, strengthens the anoxic denitrification and nitrogen removal effect, and realizes the deep nitrogen removal of the tail water; but also further degrades the residual organic matter through the O-section reaction zone to avoid the phenomenon of carbon source breakthrough.

[0029] Preferably, the first mixed filler layer includes a uniform mixed filler of zeolite, quartz sand, and volcanic rock, and a plant slow-release carbon source doped in the mixed filler.

[0030] Preferably, the plant planting layer includes fine sand and aquatic plants planted in the fine sand.

[0031] Preferably, the supporting layer is pebbles.

[0032] Preferably, the height ratio of the supporting layer, the first mixed filler layer, and the plant planting layer is 1:3:1.

[0033] Preferably, the plant slow-release carbon source is selected from reed straws.

[0034] Preferably, the aquatic plants are selected from at least one of reed, calamus, and canna.

[0035] Preferably, the aquatic plants are selected from reed.

[0036] Preferably, the volume ratio of zeolite, quartz sand, and volcanic rock is 6:3:1.

[0037] Preferably, the particle size of the zeolite is 2 mm to 4 mm.

[0038] Preferably, the particle size of the quartz sand is 2 mm to 4 mm.

[0039] Preferably, the particle size of the volcanic rock is 6 mm to 8 mm.

[0040] Preferably, the particle size of the fine sand is 1 mm to 2 mm.

[0041] Preferably, the aerobic carbon degradation zone includes, from bottom to top, a supporting layer, a second mixed filler layer, and a plant planting layer 8 arranged in sequence.

[0042] The second mixed filler layer includes a uniform mixed filler of zeolite, quartz sand, and volcanic rock;

[0043] The height ratio of the supporting layer, the second mixed filler layer and the plant planting layer is 1:3:1;

[0044] The volume ratio of the zeolite, quartz sand and volcanic rock is 6:3:1.

[0045] Preferably, the water inlet area and the water outlet area are filled with pebbles, and the particle size of the pebbles is 10 mm to 16 mm.

[0046] Preferably, the aspect ratio of the length to the width of the folded horizontal subsurface flow constructed wetland bed is 2:1, and the depth ≤ 1.5 m.

[0047] Preferably, the volume ratio of the water inlet area, the denitrification and nitrogen removal area, the aerobic carbon reduction area and the water outlet area is 1:3:1:1.

[0048] The working principle of the enhanced nitrogen removal treatment method for tail water based on constructed wetland of the present invention is as follows:

[0049] The external discharged tail water of urban sewage treatment plants has the water quality characteristics of high total nitrogen and nitrate nitrogen content and low C / N ratio. It is transported through the water inlet pipe into the water inlet area of the folded horizontal subsurface flow wetland and evenly distributed through the water inlet area into the denitrification and nitrogen removal area (main reaction area) of the constructed wetland. First, it flows through the supporting layer and the first mixed filler layer of the main reaction area from bottom to top in sequence, and fully contacts with the zeolite / quartz sand / volcanic rock mixed filler in the first mixed filler layer. The reed straw nylon bags providing organic carbon sources are randomly buried in this area. The heterotrophic microorganisms (such as denitrifying bacteria, etc.) in the attached biofilm use the reed straw and its decomposition products filled in the first mixed filler layer as biomass carbon sources to carry out heterotrophic denitrification. Using the added reed straw and its decomposition products (taking CH3COOH as an example) as energy and electron donors, its chemical formula is as follows:

[0050] 5CH3COO - +8NO3 - →4N2+10CO2+H2O+13OH -

[0051] Microorganisms such as sulfate-reducing bacteria in the biofilm mainly carry out chemoheterotrophy using plant carbon sources, and can reduce sulfate in the tail water to sulfide to obtain the energy for survival. Its chemical equation is as follows:

[0052] Ethanol+0.5SO4 2- →CH3COO - +0.5HS - +0.5H + +H2O

[0053] In the denitrification and nitrogen removal zone (A-section reaction zone), sulfide or elemental sulfur is utilized by chemolithoautotrophic microorganisms such as Thiobacillus denitrificans as an electron donor to reduce nitrate in the tail water to nitrogen gas. The chemical equation is as follows:

[0054] NO3 － +1.10S + 0.40CO2 + 0.76H2O + 0.08NH4 + →0.5N2 + 1.10SO4 2－ +1.28H + +0.08C5H7O2N

[0055] The sulfur oxidation reaction generates sulfate. Porous materials (zeolite, volcanic rock) provide a well-attached growth microenvironment for sulfur autotrophic denitrifying bacteria; in addition, they have a buffering capacity for the pH value of the wetland system. The upper part of the denitrification and nitrogen removal zone (A-section reaction zone) can effectively remove nitrogen through the action of aquatic plants such as reeds.

[0056] Sulfur autotrophic denitrifying bacteria will produce a large amount of acid through autotrophic denitrification. Through the buffering action of the alkalinity generated by heterotrophic denitrification and the addition of fillers such as zeolite, the pH of the effluent can be effectively controlled.

[0057] The removal of pollutants by aquatic plants is mainly divided into direct and indirect effects. The rich roots of aquatic plants have strong adsorption ability and can absorb a part of inorganic nitrogen from the pore water of the tail water constructed wetland bed as their own nutrients for synthesizing organic nitrogen. This part of nitrogen can be removed through the harvesting and reuse of aquatic plants, but the removal rate of this part is relatively low, not exceeding 10% - 20%, which belongs to the direct effect; in addition, the plant roots can transport oxygen to the root zone, making the root surface in an oxidized state, and ammonia nitrogen can be oxidized by nitrifying bacteria in this area to achieve the removal of most nitrogen, with a removal rate of more than 80%.

[0058] The folded-flow horizontal subsurface flow constructed wetland of the present invention uses plant carbon source, zeolite, quartz sand, and volcanic rock as reaction substrates and biofilm carriers, which are added to the tail water constructed wetland. The tail water uniformly flows into the inlet area of the constructed wetland from the inlet pipe through the water distribution pipe, and the water flow is in a downward flow. It flows into the denitrification and nitrogen removal zone (A-section reaction zone) through the holes at the bottom of the partition. After uniformly distributing the water in the supporting layer, when the tail water first flows upward through the first mixed filler layer, the filler plays a role in physically adsorbing and intercepting pollutants; heterotrophic denitrification is carried out with heterotrophic denitrifying bacteria as the dominant strain; at the same time, the reduction and re-oxidation of sulfate mediated by microorganisms are driven to achieve deep nitrogen removal by coupling heterotrophic denitrification with sulfur autotrophic denitrification, so that the removal of NO3 in the tail water -The removal of -N basically reaches 85% or more; as the water flows through the fine sand and gravel layer of the aquatic plant roots, the impurity particles in the tail water are further removed, and the growth of the plants partially removes elements such as N in the tail water. In the aerobic carbon reduction area (O-section reaction area), the water flow is downward, and heterotrophic bacteria aerobically decompose the organic matter in the effluent from the denitrification and nitrogen removal area (A-section reaction area), reducing the COD concentration of the effluent from the constructed wetland and avoiding the phenomenon of carbon source breakthrough. The water flows into the effluent area through the holes at the bottom of the partition board, and the final effluent is collected by the water distribution pipe and then discharged from the entire treatment system of the constructed wetland. The pH of the entire reaction system is maintained at about 7.0 - 8, effectively controlling the effluent pH, and the optimal reaction temperature is 20°C - 30°C.

[0059] Advantages of the present invention:

[0060] The enhanced nitrogen removal treatment method for tail water based on a constructed wetland of the present invention drives the construction of a hybrid nutrition denitrification system that combines heterotrophic denitrification and sulfur autotrophic denitrification by arranging plant slow-release carbon sources in the denitrification and nitrogen removal area of the constructed wetland and using sulfates in the tail water of the sewage treatment plant, ensuring that the treatment method has high nitrogen removal efficiency and greenhouse gas emission reduction effects. The treatment method of the present invention combines the hybrid nutrition denitrification technology with a folded-flow subsurface flow constructed wetland, effectively enhancing the deep nitrogen removal process of the tail water of sewage treatment plants with a low C / N ratio, and having the characteristics of synergistic pollution reduction and carbon reduction, with the advantages of high nitrogen removal efficiency, low carbon emission, simple management, and low operating cost, enabling the effluent pollutants including TN and COD to meet the Class IV standards of surface water.

[0061] The constructed wetland system of the present invention, without changing the structure of the horizontal subsurface flow constructed wetland, improves the hydraulic characteristics of the wetland system by installing non-equidistant partition boards inside the bed body, and constructs an A / O nitrogen removal treatment process with different volumes and functions. It not only prolongs the hydraulic retention time of the A-section reaction area, strengthens the anoxic denitrification and nitrogen removal effect, and realizes the deep nitrogen removal of the tail water; but also further degrades the residual organic matter through the O-section reaction area to avoid the phenomenon of carbon source breakthrough. It has the value of popularization and application in the field of sewage treatment technology. Description of the drawings

[0062] Figure 1 It is a schematic structural diagram of the constructed wetland system;

[0063] Among them, 1 - influent area; 2 - denitrification and nitrogen removal area; 3 - aerobic carbon reduction area; 4 - effluent area; 5 - partition board; 6 - supporting layer; 7 - first mixed filler layer; 8 - plant planting layer; 9 - aquatic plant; 10 - second mixed filler layer; 11 - influent pipe; 12 - water distribution pipe; 13 - effluent pipe. Specific implementation manners

[0064] The embodiments of the present invention will be described below with reference to the preferred embodiments. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be understood that the preferred embodiments are only for explaining the present invention, rather than limiting the protection scope of the present invention.

[0065] The present invention aims to disclose a method for enhanced denitrification treatment of tail water based on constructed wetland and a constructed wetland system, so as to solve the problems of low denitrification efficiency of the tail water of urban sewage treatment plants by traditional constructed wetlands, still relatively high total nitrogen concentration in the effluent water quality, as well as the problems of difficult management and high operation cost.

[0066] Among them, the method for enhanced denitrification treatment of tail water based on constructed wetland includes the following steps:

[0067] S1. A denitrification zone and an aerobic carbon reduction zone are arranged between the influent area and the effluent area of the constructed wetland. The denitrification zone is at least provided with a mixed packing layer, and the mixed packing layer at least includes a plant slow-release carbon source. The constructed wetland is a folded-flow subsurface flow constructed wetland;

[0068] S2. The anoxic sludge is diluted and introduced into the influent area, denitrification zone, aerobic carbon reduction zone and effluent area of the constructed wetland, and the hydraulic retention time is maintained greater than or equal to the first time under the first temperature condition, and then discharged to achieve the first-stage biofilm formation treatment;

[0069] S3. The tail water is introduced into the influent area, denitrification zone, aerobic carbon reduction zone and effluent area of the constructed wetland, and the hydraulic retention time is maintained greater than or equal to the second time under the second temperature condition to achieve the second-stage biofilm formation treatment;

[0070] S4. The tail water is introduced into the influent area, denitrification zone, aerobic carbon reduction zone and effluent area of the constructed wetland, and the hydraulic retention time is within the third time range under the third temperature condition, so that the tail water undergoes a hybrid nutrition denitrification treatment of heterotrophic denitrification and sulfur autotrophic denitrification for collaborative denitrification until the total nitrogen removal rate in the tail water reaches the standard and then is discharged.

[0071] By filling the denitrification zone of the constructed wetland with plant slow-release carbon sources and using the sulfate in the tail water of the sewage treatment plant, a hybrid nutrition denitrification system that combines heterotrophic denitrification and sulfur autotrophic denitrification is jointly driven, ensuring that the treatment method has high denitrification efficiency and greenhouse gas emission reduction effects. Through the treatment method that combines the hybrid nutrition denitrification technology with the folded subsurface flow constructed wetland, the deep denitrification process of the tail water of sewage treatment plants with a low C / N ratio is effectively strengthened, and it has the characteristics of synergistic pollution reduction and carbon reduction, with the advantages of high denitrification efficiency, low carbon emissions, simple management, and low operating costs, enabling the effluent pollutants including TN and COD to meet the Class IV standards of surface water.

[0072] Among them, during the biofilm formation process in the second stage, the effluent quality of the constructed wetland is monitored every 2 days, and the average values of the COD, TN, and NO3 - -N concentrations in the effluent are detected and calculated, and the corresponding removal rates are calculated until the removal rate of TN remains stable and is maintained at 80% or above, and then the formal tail water treatment stage can be carried out.

[0073] In some embodiments, in S3, there are at least sulfate-reducing bacteria, heterotrophic denitrifying bacteria, and autotrophic denitrifying bacteria including Thiobacillus denitrificans in the denitrification zone;

[0074] Microorganisms such as sulfate-reducing bacteria in the biofilm carry out chemoheterotrophic action using plant slow-release carbon sources to reduce the sulfate in the tail water to sulfide; sulfide or elemental sulfur is utilized by chemoautotrophic microorganisms such as Thiobacillus denitrificans as an electron donor to reduce the nitrate in the tail water to nitrogen; the autotrophic denitrifying bacteria control the effluent pH through the neutralization of the acid produced by autotrophic denitrification reaction and the alkalinity produced by heterotrophic denitrification reaction.

[0075] In some embodiments, S2 is carried out more than twice to ensure the growth of stable heterotrophic microorganisms in the biofilm in the denitrification zone.

[0076] Exemplarily, S2 is carried out 2 to 3 times to ensure the growth of stable heterotrophic microorganisms in the biofilm in the denitrification zone.

[0077] In some embodiments, the first temperature is 10°C to 30°C.

[0078] In some embodiments, the first time is 72 h.

[0079] Exemplarily, the first time is 10 days.

[0080] In some embodiments, the second temperature is 20°C to 30°C.

[0081] In some embodiments, the second time is 48 h.

[0082] Exemplarily, the second time is 20 days. The film hanging treatment time can be appropriately extended in spring and winter.

[0083] In some embodiments, the third temperature is 10°C to 35°C.

[0084] Exemplarily, the third temperature is 20°C to 30°C.

[0085] In some embodiments, the third time is 2d to 3d.

[0086] In some embodiments, in S2, the anoxic sludge is the sludge from the anoxic tank of a municipal wastewater treatment plant, and the anoxic sludge is diluted to a concentration < 1 g / L;

[0087] In some embodiments, in S3, the tail water is the secondary effluent or reclaimed water of a municipal wastewater treatment plant, the C / N ratio of the tail water ≤ 3, and the mass concentration of nitrate nitrogen (NO3 - -N) in the tail water ≤ 16 mg / L.

[0088] Exemplarily, the tail water is sewage with a low C / N ratio, and the tail water is the secondary effluent or reclaimed water of a municipal wastewater treatment plant with a C / N ratio ≤ 2 - 4.

[0089] Exemplarily, the tail water is the secondary treated effluent or reclaimed water of a municipal wastewater treatment plant with a C / N ratio ≤ 2 - 3.

[0090] Wherein, the concentration range of nitrate nitrogen (NO3 - -N) in the tail water is 8 mg / L to 16 mg / L.

[0091] In some embodiments, as Figure 1 shown, there is also provided a constructed wetland system for implementing the tail water enhanced denitrification treatment method in any of the above embodiments, which at least includes an inlet area 1, a denitrification area 2, an aerobic carbon reduction area 3, and an outlet area 4 arranged in sequence. The adjacent areas between the inlet area 1, the denitrification area (A-section reaction area) 2, the aerobic carbon reduction area (O-section reaction area) 3, and the outlet area 4 are separated by a partition 5, and all the partitions 5 are arranged in a vertically offset manner to form a folded horizontal subsurface flow constructed wetland bed;

[0092] The denitrification area 2 is an upward-flow anoxic denitrification unit. The denitrification area 2 includes, from bottom to top, a support layer 6, a first mixed filler layer 7 (plant slow-release carbon source + inorganic mixed filler), and a plant planting layer 8 arranged in sequence. Among them, the plant planting layer 8 is located at the top of the wetland, and aquatic plants 9 with well-developed roots are evenly planted thereon.

[0093] Exemplarily, the influent zone 1, denitrification and nitrogen removal zone 2, aerobic carbon degradation zone 3, and effluent zone 4 are separated by three baffles 5. In the upper middle part between the influent zone 1 and the denitrification and nitrogen removal zone (A-section reaction zone) 2, a baffle 5 is provided, and holes allowing water flow are provided in the lower part; between the denitrification and nitrogen removal zone (A-section reaction zone) 2 and the aerobic carbon degradation zone (O-section reaction zone) 3, a baffle 5 is provided, and water flows from the denitrification and nitrogen removal zone (A-section reaction zone) 2 into the aerobic carbon degradation zone (O-section reaction zone) 3 through the plant planting layer 8; in the upper middle part between the aerobic carbon degradation zone (O-section reaction zone) 3 and the effluent zone 4, a baffle 5 is provided, and holes allowing water flow are provided in the lower part. The bottom of the influent zone 1 is connected to the denitrification and nitrogen removal zone (A-section reaction zone) 2 through the lower holes of the baffle 5, the denitrification and nitrogen removal zone (A-section reaction zone) 2 is connected to the water flow of the aerobic carbon degradation zone (O-section reaction zone) 3 through the plant planting layer 8, and the bottom of the aerobic carbon degradation zone (O-section reaction zone) 3 is connected to the effluent zone 4 through the lower holes of the baffle 5, so as to obtain a folded horizontal subsurface flow constructed wetland bed body.

[0094] Among them, when treating the tail water of an urban sewage treatment plant with the folded horizontal subsurface flow constructed wetland bed body, the tail water is introduced into the influent zone 1 from the influent pipe 11 at the upper part of the influent zone 1 of the folded horizontal subsurface flow constructed wetland bed body. The water flows downward. In the denitrification and nitrogen removal zone (A-section reaction zone) 2, the water flows from bottom to top, successively flowing through the support layer 6, the first mixed filler layer 7, and the plant planting layer 8, and completing the heterotrophic denitrification coupled with sulfur-based autotrophic denitrification nitrogen removal treatment driven by the plant slow-release carbon source and the sulfate in the influent water. The water flow after the anoxic nitrogen removal treatment flows into the aerobic carbon degradation zone (O-section reaction zone) 3 through the round holes on the baffle 5 at the upper part of the denitrification and nitrogen removal zone (A-section reaction zone) 2. The water flows from top to bottom, successively flowing through the plant planting layer 8, the second mixed filler layer 10, and the support layer 6, and completing the aerobic carbon oxidation treatment, and then flows into the effluent zone 4 from the bottom, and is uniformly collected from the upper part of the effluent zone 4 by the water distribution pipes uniformly distributed, and flows out of the constructed wetland bed body after flowing into the effluent pipe 13. During this process, the membrane hanging treatment of the folded subsurface flow constructed wetland is carried out until the effluent quality of the constructed wetland is maintained stable, and the total nitrogen removal rate of the tail water reaches and remains at 80% and above, which is acceptable.

[0095] Among them, the influent pipe 11 and the effluent pipe 13 are respectively arranged at both ends of the constructed wetland in the horizontal direction.

[0096] The tail water flows into the water inlet area 1 through the water inlet pipe 11, and is evenly distributed to the water inlet area 1 of the constructed wetland through the water distribution pipe laid on the upper part of the water inlet area 1; the tail water flows into the denitrification and nitrogen removal area (A-section reaction area) 2 by folding from the bottom of the water inlet area 1, and flows through the denitrification and nitrogen removal area (A-section reaction area) 2 and the aerobic carbon reduction area (O-section reaction area) 3 in the forms of upward flow and downward flow respectively; then it flows into the water outlet area 4 from the supporting layer 6 at the bottom of the aerobic carbon reduction area (O-section reaction area) 3, and the treated tail water of the constructed wetland is evenly and quickly collected through the water distribution pipe laid in the upper middle part of the water outlet area 4, and finally is smoothly discharged from the constructed wetland through the water outlet pipe.

[0097] The pipe diameter of the water inlet pipe 11 is determined by hydraulic calculation according to the total treatment water volume of the system.

[0098] Two rows of water distribution holes with pore diameters of 2 - 10 mm are evenly arranged at the bottom of the water distribution pipe 12, and the included angle of the center lines of the holes is 45°.

[0099] The water distribution pipe 12 is laid at a position 10 cm - 15 cm away from the upper surface of the water inlet area 1, preferably at 10 cm.

[0100] The pipe diameter of the water distribution pipe is determined by hydraulic calculation according to the total treatment water volume of the system.

[0101] Two rows of water distribution holes with pore diameters of 2 mm - 10 mm are evenly arranged at the bottom of the water distribution pipe, and the included angle of the center lines of the holes is 45°.

[0102] The water distribution pipe is laid at a position 15 cm - 20 cm away from the upper surface of the water outlet area 4, preferably at 15 cm.

[0103] The bed body of the folded horizontal subsurface flow constructed wetland is in a cuboid configuration.

[0104] In some embodiments, the first mixed filler layer 7 includes a uniform mixed filler of zeolite, quartz sand and volcanic rock, and a plant slow-release carbon source doped in the mixed filler.

[0105] In some embodiments, the plant planting layer 8 includes fine sand and aquatic plants 9 planted in the fine sand.

[0106] In some embodiments, the supporting layer 6 is pebbles.

[0107] In some embodiments, the height ratio of the supporting layer 6, the first mixed filler layer 7 and the plant planting layer 8 is 1:3:1.

[0108] Among them, the fine sand is the fine sand for plant planting. The plant slow-release carbon source doped in the mixed filler is reed straw packaged in a nylon small bag.

[0109] The preparation method of the plant slow-release carbon source is as follows: Cut the reed straw into small sections of 1 cm to 2 cm, soak it in alkali for 24 hours, then rinse it with tap water and dry it for later use; Every 20 g of the pretreated reed straw is packed into a small nylon bag (with a pore size of 1 mm) as the plant slow-release carbon source.

[0110] Exemplarily, the plant slow-release carbon source is selected from reed straw.

[0111] In some embodiments, the aquatic plant 9 is selected from at least one of reed, calamus, cyperus alternifolius, and canna indica.

[0112] Exemplarily, the aquatic plant 9 is selected from reed.

[0113] In some embodiments, the planting density of the aquatic plant 9 is 10 - 30 plants / m 2 .

[0114] Exemplarily, the planting density of the aquatic plant 9 is 20 plants / m 2 .

[0115] Among them, the aquatic plant 9 planted in the plant planting area has well-developed roots, has a certain oxygen transport capacity, and is a plant with relatively strong impact load resistance. An aerobic microenvironment is formed around the plant roots, which is beneficial to the growth of aerobic bacteria, and thus is beneficial to the removal of ammonia nitrogen and organic matter in the tail water. In the plant planting area, through the oxygen secretion and oxygen transmission of the plant roots, the upper surface of the substrate layer is in a state of relatively high DO, providing a favorable living environment for the organic matter-degrading microorganisms. The tail water flows through the hybrid nutrition denitrification and nitrogen removal area driven by both the reed straw as the carbon source and the products of sulfate reduction in the influent. A large amount of nitrate nitrogen and total nitrogen in the tail water are removed. Then the tail water passes through the upper part of the substrate layer, the plant root zone, and the O-section carbon oxidation and degradation area, and finally the residual organic matter in the water body is further deeply removed.

[0116] In some embodiments, the volume ratio of zeolite, quartz sand, and volcanic rock is 6:3:1.

[0117] In some embodiments, the particle size of the zeolite is 2 mm to 4 mm.

[0118] In some embodiments, the particle size of the quartz sand is 2 mm to 4 mm.

[0119] In some embodiments, the particle size of the volcanic rock is 6 mm to 8 mm.

[0120] In some embodiments, the particle size of the fine sand and gravel is 1 mm to 2 mm.

[0121] In some embodiments, the aerobic carbon reduction zone 3 is a downward-flow aerobic carbon oxidation unit. The aerobic carbon reduction zone 3 includes, from bottom to top, a supporting layer 6, a second mixed packing layer 10, and a plant planting layer 8 arranged in sequence; the plant planting layer 8 is located at the top of the wetland, and aquatic plants 9 with well-developed root systems are evenly planted thereon;

[0122] The second mixed packing layer 10 includes a uniformly mixed packing of zeolite, quartz sand, and volcanic rock;

[0123] The height ratio of the supporting layer 6, the second mixed packing layer 10, and the plant planting layer 8 is 1:3:1;

[0124] The volume ratio of zeolite, quartz sand, and volcanic rock is 6:3:1.

[0125] In some embodiments, the inlet zone 1 and the outlet zone 4 are filled with pebbles, and the particle size of the pebbles is 10 mm to 16 mm.

[0126] In some embodiments, the aspect ratio of the length to the width of the folded horizontal subsurface flow constructed wetland bed is 2:1, and the depth ≤ 1.5 m;

[0127] In some embodiments, the volume ratio of the inlet zone 1, the denitrification and nitrogen removal zone 2, the aerobic carbon reduction zone 3, and the outlet zone 4 is 1:3:1:1.

[0128] In some embodiments, in the denitrification and nitrogen removal zone 2, the volume ratio of the plant planting layer 8 to the total volume of the constructed wetland is 1:10; the volume ratio of the first mixed packing layer 7 to the total volume of the constructed wetland is 3:10; the total volume ratio of the supporting layer 6 to the total volume of the constructed wetland is 1:10. The height ratio of the first mixed packing layer 7 to the constructed wetland is 1:2. The height ratio of the supporting layer 6 to the constructed wetland is 1:6.

[0129] In some embodiments, in the aerobic carbon reduction zone 3, the volume ratio of the plant planting layer 8 to the total volume of the constructed wetland is 1:30; the volume ratio of the second mixed packing layer 10 to the total volume of the constructed wetland is 1:10, and the total volume ratio of the supporting layer 6 to the total volume of the constructed wetland is 1:30. The height ratio of the plant planting layer 8 to the constructed wetland is 1:5. The height ratio of the second mixed packing layer 10 to the constructed wetland is 1:2.

[0130] Exemplarily, taking the total height of the constructed wetland as 120 cm (the height of the bed body is 100 cm) as an example, the height of the first partition board 5 arranged longitudinally along the bed body is 100 cm, and the bottom of it is 15 cm away from the bottom of the pond; the height of the second partition board 5 is 100 cm, and water passing round holes are evenly arranged laterally within the range of 20 cm at the top of the partition board 5, and its bottom has no gap with the bottom of the pond; the height of the third partition board 5 is 100 cm, and the bottom of it is 15 cm away from the bottom of the pond. The height of the plant planting layer 8 in the denitrification and nitrogen removal area (A-section reaction area) 2 is 20 cm, the height of the first mixed filler layer 7 is 60 cm, and the height of the supporting layer 6 is 20 cm. The height of the plant planting layer 8 in the aerobic carbon reduction area (O-section reaction area) 3 is 20 cm, the height of the second mixed filler layer 10 is 60 cm, and the height of the supporting layer 6 is 20 cm. Other heights of the constructed wetland are also applicable, and the heights of the plant planting layer 8, the first mixed filler layer 7, the second mixed filler layer 10, and the supporting layer 6 are set according to the corresponding ratios.

[0131] In order to make the technical problems, technical solutions and beneficial effects solved by this application clearer, the following will further describe in detail the tail water enhanced denitrification treatment method and constructed wetland system of the present invention based on specific embodiments and drawings. Obviously, the specific embodiments described are only a part of the embodiments of this application, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and in no way constitutes a limitation to this application and its application. Based on the specific embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of this application.

[0132] For those specific technologies or conditions not specified in the specific embodiments, they shall be carried out according to the technologies or conditions described in the literature in this field or according to the product specifications. For the reagents or instruments not specified for the manufacturers, they are all conventional products that can be obtained through commercial purchase.

[0133] Example 1

[0134] A constructed wetland system includes:

[0135] As Figure 1 shown, a folded-flow horizontal subsurface flow coupled hybrid nutrition denitrification tail water constructed wetland system is constructed. This constructed wetland system is located in a certain area of Jinzhong City, Shanxi Province, and uses a folded-flow horizontal subsurface flow constructed wetland with a treatment scale of 3000 m 3 / d to deeply treat the tail water of a sewage treatment plant with a low C / N ratio.

[0136] In this embodiment, the overall height of the constructed wetland bed is 100 cm, the height of the supporting layer 6 is 20 cm, the heights of the first mixed filler layer 7 and the second mixed filler layer 10 are 60 cm, and the height of the plant planting layer 8 is 20 cm for illustration purposes; this embodiment is applicable to other constructed wetlands with a height ≤ 1.6 m.

[0137] In this embodiment, the surface hydraulic loading of the constructed wetland is 0.375 m 3 / (m 2 ·d), the project covers an area of 0.8 hectares (ha), and is divided into 40 units in total. According to the terrain, the wetland units are designed as rectangles with a unit plane size of 20 m × 10 m. The sizes and structures of each unit are the same. There is a 200 mm cast-in-place reinforced concrete enclosure around each unit, with a depth of 1.0 m, an effective water depth of 0.95 m, a pool body superheight of 0.3 m, and an overall height of 1.3 m. The pool body is 0.3 m above the ground, and the hydraulic gradient at the bottom of the pool is 0.5%. A 100 mm thick C10 concrete cushion is set at the bottom of the pool, and the anti-seepage of the pool body adopts a composite geomembrane in the form of two layers of fabric and one layer of film.

[0138] The constructed wetland is evenly distributed with water through a water conveyance channel.

[0139] In this embodiment, the total area of the constructed wetland is 0.8 ha, and the area of a single unit is 200 m 2 ; thus, it is divided into 40 units in total. Each unit needs to be equipped with a water conveyance channel, and the length of the water conveyance channel is about 410 m. The spacing between adjacent water distribution perforated pipes is 1 m, the diameter of the perforated pipes is 100 mm, and the aperture of the water distribution (collection) perforated pipes is 20 mm.

[0140] Construction of the folded horizontal subsurface flow constructed wetland:

[0141] S1. Excavate the constructed wetland bed

[0142] At the site of the tail water to be treated, excavate a subsurface flow constructed wetland bed with a depth of 1.5 m, and conduct construction such as structural anti-seepage and laying of anti-seepage materials at the bottom of the pool. Use the original soil or reinforced concrete to construct the pool body around the wetland.

[0143] S2. Install vertical partition boards

[0144] In each unit of the constructed wetland, install three concrete precast partition boards along the length direction, with distances of 3.33 m, 10 m, 3.33 m, and 3.33 m from each other, dividing the wetland unit into an influent zone 1, a denitrification and nitrogen removal zone (A-section reaction zone) 2, an aerobic carbon reduction zone (O-section reaction zone) 3, and an effluent zone 4.

[0145] S3. Selection and preparation of fillers

[0146] S31. Mix 200 bags of reed straw carbon packs (0.5 kg / bag) evenly with zeolite with a particle size of 20 - 40 mm, quartz sand with a particle size of 20 - 40 mm, and volcanic rock with a particle size of 60 - 80 mm to prepare the filler for the denitrification and nitrogen removal area (A-section reaction area) 2, namely reed straw / zeolite / quartz sand / volcanic rock filler. The volume ratio of zeolite, quartz sand, and volcanic rock particles is 6:3:1. Select pebbles with a particle size of 100 - 160 mm as the filler for the supporting layer. Select fine sand and gravel with a particle size of 10 - 20 mm as the filler for the plant planting layer.

[0147] S32. Mix evenly zeolite with a particle size of 20 - 40 mm, quartz sand with a particle size of 20 - 40 mm, and volcanic rock with a particle size of 60 - 80 mm to prepare the filler for the aerobic carbon reduction area (O-section reaction area) 3, namely zeolite / quartz sand / volcanic rock filler. The volume ratio of zeolite, quartz sand, and volcanic rock particles is 6:3:1. Select pebbles with a particle size of 100 - 160 mm as the filler for the supporting layer. Select fine sand and gravel with a particle size of 10 - 20 mm as the filler for the plant planting layer.

[0148] S33. Select pebbles with a particle size of 100 - 160 mm as the filler for the wetland unit inlet area 1 and the outlet area 4.

[0149] S4. Fill the filler and lay the constructed wetland bed

[0150] S41. Uniformly lay the water distribution pipe 13 in the inlet area of the constructed wetland bed, that is, uniformly lay the water distribution pipe 13 at a height of (10 ± 1) cm from the top of the pebble filler area. The water distribution pipe 13 is connected to the water inlet pipe 11. The diameter of the water distribution pipe is 20 cm, and water distribution holes are uniformly arranged on the water distribution pipe with a hole diameter of (10 ± 1) mm. The tail water flows out evenly from the water distribution holes, facilitating the uniform inflow of the tail water into the constructed wetland. Uniformly lay the water distribution pipe in the outlet area, that is, uniformly lay the water distribution pipe at a height of (20 ± 1) cm from the top of the pebble filler area. The diameter of the water distribution pipe is 20 cm, and water collection holes are uniformly arranged on the water distribution pipe with a hole diameter of (10 ± 1) mm. The treated tail water is collected through the water collection holes, converges into the water distribution pipe, and is smoothly discharged through the outlet pipe;

[0151] S42. Fill the pebbles, mixed filler, and fine sand and gravel in the constructed wetland bed from bottom to top in sequence to obtain the constructed wetland bed body. Among them, the height ratio of the supporting layer to the height of the constructed wetland bed is 1:5; the height ratio of the matrix layer to the height of the constructed wetland bed is 3:5; the height ratio of the plant planting layer to the height of the constructed wetland bed is 1:5;

[0152] S43. Lay fine sand and gravel on the top of the matrix layer to form an aquatic plant planting layer, and plant oxygen-transporting plants with well-developed roots on the planting layer; The oxygen-transporting plants are selected from one or more of the plants with relatively strong shock load resistance such as reed, Cyperus alternifolius, and calamus. The planting density of the plants is 20 plants / m2 。

[0153] Among them, the mixed planting of plants is beneficial to the removal of pollutants and the reduction of greenhouse gas emissions, achieving the synergistic effect of pollution reduction and carbon reduction in constructed wetlands.

[0154] The first mixed packing layer 7 of the denitrifying and nitrogen-removing zone (A-section reaction zone) 2: Sulfate in the tail water first undergoes a reduction reaction mediated by sulfate-reducing bacteria (SRB), and the reaction product (reduced sulfur) serves as the main substrate for autotrophic denitrification and is the electron donor for sulfur autotrophic denitrification.

[0155] Reed straw-zeolite-volcanic rock-quartz sand layer: The addition of reed straw is to provide biomass carbon source for the denitrification of heterotrophic bacteria, and the purpose of adding zeolite, volcanic rock and quartz sand is to provide an attachment carrier for the growth of microorganisms.

[0156] Heterotrophic denitrification mainly fills the system with plant slow-release carbon source as energy and electron donor.

[0157] Example 2

[0158] A method for enhanced nitrogen removal of tail water using the constructed wetland in Example 1, comprising the following steps:

[0159] S1. First-stage biofilm formation treatment

[0160] Dilute the sludge from the anoxic tank of the urban sewage treatment plant to a concentration < 1 g / L, introduce it from the inlet pipe 11 into the inlet area 1 of the constructed wetland, flow through the denitrifying and nitrogen-removing zone (A-section reaction zone) 2 and the aerobic carbon-reducing zone (O-section reaction zone) 3 in sequence, and the water flows upward to the outlet area 4 of the constructed wetland. Under the condition of a temperature of 10°C to 30°C, maintain a hydraulic retention time ≥ 3 d, and discharge it from the outlet pipe out of the constructed wetland for the first-stage biofilm formation treatment; this process is continuously carried out 2 to 3 times.

[0161] Among them, the removal of pollutants from the tail water of the sewage treatment plant in the first stage of biofilm formation treatment is mainly divided into the adsorption stage of the mixed packing and the preliminary cultivation stage of nitrogen-removing functional microorganisms. Among them, the nitrogen-removing functional microorganisms include but are not limited to autotrophic denitrifying bacteria such as Thiobacillus denitrificans and heterotrophic denitrifying bacteria.

[0162] S2. Second-stage biofilm formation treatment

[0163] After the first-stage biofilm formation treatment, the C / N ratio of the urban sewage treatment plant ≤ 3, NO3 -The tail water with - N mass concentration ≤ 16 mg / L is introduced from the inlet pipe into the influent area 1 of the constructed wetland, and flows through the denitrification and nitrogen removal area (A - section reaction area) 2 and the aerobic carbon - reduction area (O - section reaction area) 3 in sequence. The water flows upward to the effluent area 4 of the constructed wetland and is discharged from the constructed wetland through the distribution pipe and the outlet pipe. Under the condition that the temperature is 20°C - 30°C, the hydraulic retention time is maintained ≥ 48 h for the second - stage biofilm formation treatment.

[0164] Among them, during the second - stage biofilm formation treatment, the effluent quality of the constructed wetland is monitored every 3 days, and the average values of COD, TN, and NO3 - - N concentration in the effluent are detected and calculated, and the corresponding removal rates are calculated until the removal rate of TN remains stable and is maintained above 80%, until the effluent quality is stable, then the constructed wetland for enhanced nitrogen removal of the tail water of the urban sewage treatment plant with successful biofilm formation is obtained.

[0165] S3. After the biofilm formation of the folded - flow subsurface - flow constructed wetland is successful, a large number of heterotrophic denitrifying bacteria attached to the first mixed packing layer 7 in the denitrification and nitrogen removal area (A - section reaction area) 2 carry out heterotrophic denitrification and nitrogen removal microbial treatment using the carbon source provided by reed straw. The CO2 generated during this process is beneficial to the creation of an anaerobic micro - environment and can provide a certain alkalinity for the sulfur autotrophic denitrification and nitrogen removal process, which can ensure the stability of the pH of the tail water in the device.

[0166] In this embodiment, the heterotrophic denitrification and sulfur autotrophic denitrification of the folded - flow horizontal subsurface - flow constructed wetland are combined to remove nitrate in the tail water and achieve the emission reduction of N2O. Since sulfur autotrophic denitrifying microorganisms such as Thiobacillus denitrificans grow slowly and their proliferation rate is much lower than that of heterotrophic denitrifying bacteria, and the sludge production rate is low. Therefore, while maintaining a high denitrification and nitrogen removal efficiency, this constructed wetland system will not cause the clogging of the wetland system due to the large - scale reproduction of biofilm sludge.

[0167] The aquatic plants planted in the plant planting area of this embodiment are a certain amount of economic plants, which have a certain economic value.

[0168] To sum up,

[0169] The method for enhanced nitrogen removal of tail water of the present invention adds small sections of pretreated reed straw as a plant - slow - release carbon source to the mixed packing, which not only realizes the resource utilization of plant litter, but also improves the nitrogen removal efficiency of the tail water while reducing the operation cost of the treatment system. And the constructed mixed - nutrition denitrification and nitrogen removal system can not only achieve the deep removal of nitrogen - containing pollutants, but also reduce the emission of nitrous oxide (N2O), achieving the coordinated emission reduction of water - air pollutants in the constructed wetland and realizing the purpose of reducing pollution, lowering carbon, improving quality, and increasing efficiency.

[0170] The post-treatment method for enhanced denitrification of the present invention effectively stimulates the reduction and re-oxidation of sulfate in the tail water mediated by microorganisms, and then establishes a coupled system of electron donors. That is, the plant carbon source and sulfate in the tail water are used together to drive the synergistic denitrification of heterotrophic denitrification and sulfur-based autotrophic denitrification, and a hybrid nutrition denitrification system and treatment system are constructed. Moreover, it has a high denitrification efficiency, a high removal rate of total nitrogen and nitrate, especially a high removal efficiency of nitrate nitrogen. The removal rate of nitrate nitrogen reaches more than 75% under the condition of lower air temperature, and the removal rate of nitrate nitrogen reaches more than 85% under the condition of higher air temperature.

[0171] The constructed wetland system of the present invention, without changing the structure of the horizontal subsurface flow constructed wetland, improves the hydraulic characteristics of the wetland system by installing non-equidistant partitions inside the bed body, and constructs A / O denitrification treatment processes with different volumes and functions. It not only prolongs the hydraulic retention time of the A-section reaction zone, strengthens the anoxic denitrification, and realizes the deep denitrification of the tail water, but also further degrades the residual organic matter through the O-section reaction zone to avoid the phenomenon of carbon source breakthrough.

[0172] The constructed wetland system of the present invention has the characteristics of simple construction, operation and management of the constructed wetland, strong anti-impact load capacity, stable treatment effect of the effluent total nitrogen (TN), and can meet the water quality requirements for discharge or resource utilization. It has the popularization and application value in the field of sewage treatment technology.

[0173] The above embodiments are only the preferred embodiments given to fully illustrate the present invention, and the protection scope of the present invention is not limited thereto. Equivalent substitutions or transformations made by those skilled in the art on the basis of the present invention are within the protection scope of the present invention.

Claims

1. A tailwater enhanced denitrification treatment method based on artificial wetlands, characterized in that: The following steps are involved: S1. A denitrification and denitrification zone and an aerobic carbon reduction zone are set between the water inlet and outlet of the artificial wetland. The denitrification and denitrification zone is provided with at least a mixed filler layer, and the mixed filler layer includes at least a plant slow-release carbon source. The artificial wetland is a baffled submerged flow artificial wetland; S2, diluting the sludge from the anoxic tank of the sewage treatment plant and introducing it into the inlet area, denitrification and denitrification area, aerobic carbon reduction area and effluent area of ​​the artificial wetland, and keeping the hydraulic retention time greater than or equal to the first time under the first temperature condition, and then discharging it to achieve the first stage biofilm treatment; the first time is 72h; S3, introducing the tail water of the sewage treatment plant into the inlet area, denitrification and denitrification area, aerobic carbon reduction area and outlet area of ​​the artificial wetland, and maintaining the hydraulic retention time greater than or equal to the second time under the second temperature condition to achieve the second stage biofilm treatment; the second time is 48h; S4, introducing the tail water into the water inlet area, the denitrification and denitrification area, the aerobic carbon reduction area and the water outlet area of ​​the artificial wetland, and maintaining the hydraulic retention time within the third time range under the third temperature condition, so that the tail water is treated by the mixed nutrient denitrification and denitrification system under the synergistic action of heterotrophic denitrification and sulfur autotrophic denitrification, until the total nitrogen removal rate in the tail water reaches the standard and then discharged; The third time is 2d~3d; In the S3, at least sulfate-reducing bacteria, heterotrophic denitrifying bacteria and autotrophic denitrifying bacteria including denitrifying Thiobacillus are enriched and grown in the denitrification and denitrification zone; wherein the sulfate-reducing bacteria, denitrifying Thiobacillus and autotrophic denitrifying bacteria are obtained by enrichment and growth during the second-stage biofilm treatment process; the tail water is the secondary effluent or reclaimed water of a municipal sewage treatment plant, the C / N ratio of the tail water is ≤3, and the mass concentration of nitrate nitrogen in the tail water is ≤16 mg / L; Sulfate-reducing bacteria in the biofilm use the slow-release carbon source from plants to perform chemoheterotrophy to reduce sulfate in the tail water to sulfide; sulfide or elemental sulfur is used by denitrifying Thiobacillus as an electron donor to reduce nitrate in the tail water to nitrogen gas; Autotrophic denitrifying bacteria, including Thiobacillus denitrificans, control effluent pH by neutralizing the acid produced by autotrophic denitrification and the alkalinity produced by heterotrophic denitrification.

2. The tailwater enhanced denitrification treatment method based on artificial wetlands according to claim 1, characterized in that: The S2 is continuously performed for more than two times to ensure the growth of stable heterotrophic microorganisms in the biofilm of the denitrification zone.

3. The tailwater enhanced denitrification treatment method based on artificial wetlands according to claim 1, characterized in that: The first temperature is 10°C to 30°C; And / or, the second temperature is 20°C to 30°C; And / or, the third temperature is 10°C~35°C.

4. The tailwater enhanced denitrification treatment method based on artificial wetlands according to claim 1, characterized in that: In the S2, the anoxic sludge is the sludge from the anoxic tank of the urban sewage treatment plant, and the anoxic sludge is diluted to a concentration of <1 g / L.

5. An artificial wetland system for implementing the tail water enhanced denitrification treatment method according to any one of claims 1 to 4, characterized in that: The invention comprises at least an inlet area (1), a denitrification and denitrification area (2), an aerobic carbon reduction area (3) and an outlet area (4) which are arranged in sequence, wherein each adjacent area of ​​the inlet area (1), the denitrification and denitrification area (2), the aerobic carbon reduction area (3) and the outlet area (4) is separated by a partition (5), and all the partitions (5) are arranged in an up-down staggered manner to form a baffled horizontal subsurface flow artificial wetland bed; The denitrification and denitrification zone (2) comprises, from bottom to top, a supporting layer (6), a first mixed filler layer (7) and a plant planting layer (8) which are arranged in sequence.

6. The artificial wetland system according to claim 5, characterized in that: The first mixed filler layer (7) comprises a mixed filler of zeolite, quartz sand and volcanic rock, and a plant slow-release carbon source doped in the mixed filler; And / or, the plant planting layer (8) includes fine sand and gravel and aquatic plants (9) planted in the fine sand and gravel; And / or, the supporting layer (6) is pebbles; And / or, the height ratio of the supporting layer (6), the first mixed filler layer (7) and the plant planting layer (8) is 1:3:

1.

7. The artificial wetland system according to claim 6, characterized in that: The plant slow-release carbon source is selected from reed straw; and / or, the aquatic plant (9) is at least one selected from reed, calamus and canna; And / or, the volume ratio of the zeolite, quartz sand and volcanic rock is 6:3:1; And / or, the particle size of the zeolite is 2 mm to 4 mm; And / or, the particle size of the quartz sand is 2 mm to 4 mm; And / or, the particle size of the volcanic rock is 6 mm to 8 mm; And / or, the particle size of the fine sand is 1 mm to 2 mm.

8. The artificial wetland system according to claim 5, characterized in that: The aerobic carbon reduction zone (3) comprises, from bottom to top, a supporting layer (6), a second mixed filler layer (10) and a plant planting layer (8) which are arranged in sequence; The second mixed filler layer (10) comprises a mixed filler of zeolite, quartz sand and volcanic rock; The height ratio of the supporting layer (6), the second mixed filler layer (10) and the plant planting layer (8) is 1:3:1; The volume ratio of the zeolite, quartz sand and volcanic rock is 6:3:1; And / or, the water inlet area (1) and the water outlet area (4) are filled with pebbles, and the particle size of the pebbles is 10 mm to 16 mm.

9. The artificial wetland system according to claim 6, characterized in that: The baffled horizontal subsurface flow artificial wetland bed has a length-to-width ratio of 2:1 and a depth of ≤1.5m; And / or, the volume ratio of the water inlet zone (1), the denitrification and denitrification zone (2), the aerobic carbon reduction zone (3) and the water outlet zone (4) is 1:3:1:1.

Images