Natural reoxygenation enhanced nitrogen and phosphorus removal cascade artificial wetland system

Abstract

The invention relates to the technical field of constructed wetlands, in particular to a natural reoxygenation enhanced nitrogen and phosphorus removal cascade constructed wetland system. The system is provided with a first-stage constructed wetland, a second-stage ecological pond and a third-stage constructed wetland which are sequentially connected in a falling manner, wetland plants are planted in the first-stage constructed wetland and the third-stage constructed wetland; ecological pond plants are planted in the second-stage ecological pond through floating rafts, non-woven fabric is arranged below the floating rafts, and microalgae are enriched on the non-woven fabric; a mixed matrix of volcanic rock, zeolite and magnesite is arranged in the first-stage constructed wetland, a mixed matrix of volcanic rock and zeolite is arranged in the third-stage constructed wetland, and the effluent part of the second-stage ecological pond flows back to the front end of the first-stage constructed wetland. By means of a series of treatment modes, removal of nitrogen and phosphorus is enhanced, the removal rates of ammonia nitrogen, nitrate nitrogen, total nitrogen, COD and total phosphorus can reach 98.8%, 99.2%, 99.0%, 93.52% and 94.0% respectively, and the method has wide application prospects.

Description

Technical Field

[0001] The invention relates to the technical field of artificial wetlands, and in particular to a cascade artificial wetland system for natural reoxygenation and enhanced denitrification and phosphorus removal. Background Art

[0002] The traditional artificial wetland-ecological pond combination technology uses the anaerobic / anoxic-aerobic process of the artificial wetland itself to achieve the removal of ammonia nitrogen in the nitrification process and nitric nitrogen in the denitrification process. At the same time, it uses the adsorption effect of the matrix to fix phosphorus in the matrix, and then uses the absorption effect of plants in the ecological pond to further remove nitrogen and phosphorus pollutants in the sewage.

[0003] However, because artificial wetlands have been flooded with sewage for a long time, the dissolved oxygen in them is seriously insufficient, which often leads to excessive ammonia nitrogen in the effluent. Eco-ponds are mostly used as ecological landscapes, and the nitrogen and phosphorus removed by plants are less than 10%, making the nitrogen and phosphorus removal efficiency of the artificial wetland-ecological pond combination technology low. The problem of low dissolved oxygen can be improved to a certain extent by installing aeration devices or fountains in the ecological ponds. However, this method requires a lot of investment and brings complexity to process maintenance.

[0004] Therefore, the present invention proposes a multi-stage artificial wetland-ecological pond system, which, on the one hand, constructs an "anoxic-aerobic-anoxic" environment by backflow, and on the other hand, adjusts the composite matrix to achieve simultaneous enhanced removal of nitrogen, phosphorus, COD, etc., and greatly reduces investment and maintenance costs, and has broad application prospects. Summary of the invention

[0005] The purpose of the present invention is to provide a cascade artificial wetland system for natural reoxygenation enhanced denitrification and phosphorus removal, so as to solve the problem of low ammonia nitrogen removal efficiency of existing artificial wetland systems.

[0006] To achieve the above object, the present invention adopts the following technical scheme: a cascade artificial wetland system for natural reoxygenation to enhance denitrification and phosphorus removal, comprising a first-level artificial wetland, a second-level ecological pond and a third-level artificial wetland connected in sequence;

[0007] Wetland plants are planted in the first-level artificial wetland and the third-level artificial wetland, and ecological pond plants are planted in the second-level ecological pond;

[0008] The first-stage artificial wetland is provided with a first gravel layer and a first matrix layer, and the first matrix layer is a mixture of volcanic rock, zeolite and magnesite;

[0009] The second-level ecological pond is provided with a second gravel layer, a non-woven fabric and a float valve are fixed above the second-level ecological pond, microalgae are enriched on the non-woven fabric, and ecological pond plants are planted on the float valve;

[0010] The third-level artificial wetland is provided with a third gravel layer and a second matrix layer, and the second matrix layer is a mixture of volcanic rock and zeolite;

[0011] The outflow of the second-stage ecological pond flows back to the front end of the first-stage artificial wetland.

[0012] Furthermore, the area ratio of the first-level artificial wetland, the second-level ecological pond and the third-level artificial wetland is 1:0.5~1:0.5~1; in the first-level artificial wetland and the third-level artificial wetland, the water level is controlled at 0~10cm below the substrate layer; the hydraulic retention time is 24~48h; and the return ratio of the second-level ecological pond effluent is 100~200%.

[0013] Furthermore, the particle sizes of gravel in the first gravel layer, the second gravel layer and the third gravel layer are all 2-3 cm; the particle sizes of volcanic rock, zeolite and magnesite in the first matrix layer are all 1-2 cm, and the volume ratio of volcanic rock, zeolite and magnesite is 1:1:1; the particle sizes of volcanic rock and zeolite in the second matrix layer are all 1-2 cm, and the volume ratio of volcanic rock to zeolite is 1:1.

[0014] Furthermore, the wetland plants are rooted in the substrate layer, and the wetland plants include yellow iris, iris, reed and canna, with a planting density of 90 to 110 plants / m 2 .

[0015] Furthermore, the roots of the eco-pond plants are rooted in the water through the non-woven fabric. The eco-pond plants include cattail, iris and calamus, with a planting density of 40 plants / m 2 .

[0016] Furthermore, the first-level artificial wetland is provided with a first baffle and a second baffle on the water inlet side and the water outlet side, respectively, the first gravel layer and the first matrix layer are located between the first baffle and the second baffle, and the first baffle and the second baffle are baffles with holes; a third baffle and a fourth baffle are provided on the water inlet side and the water outlet side of the second-level ecological pond, respectively, the second gravel layer is located behind the water inlet side of the third baffle, and the fourth baffle is located above the second gravel layer, the third baffle is a baffle with holes, and the fourth baffle is a baffle without holes; a fifth baffle and a sixth baffle are provided on the water inlet side and the water outlet side of the third-level artificial wetland, respectively, the third gravel layer and the second matrix layer are located between the fifth baffle and the sixth baffle, the fifth baffle is a baffle with holes, the lower side of the sixth baffle is a baffle with holes, and the upper side is a baffle without holes, and the height of the baffle with holes on the lower side of the sixth baffle is consistent with the height of the third gravel layer.

[0017] Furthermore, the water inlet of the first-level artificial wetland is located in the middle of the water inlet side, and the water outlet is located above the water outlet side, and the water outlet falls into the second-level ecological pond; the water inlet of the second-level ecological pond is located above the water inlet side, and the water outlet is located above the water outlet side, and the water outlet falls into the third-level artificial wetland; the water inlet of the third-level artificial wetland is located above the water inlet side, and the water outlet is located above the water outlet side.

[0018] Furthermore, the artificial wetland system can achieve an ammonia nitrogen removal rate of 98.8%, a nitrate nitrogen removal rate of 99.2%, a total nitrogen removal rate of 99.0%, a COD removal rate of 93.52%, and a total phosphorus removal rate of 94.0%.

[0019] Beneficial effects of the present invention:

[0020] 1. The present invention solves the problem of low ammonia nitrogen removal efficiency in traditional artificial wetlands; during the process, the dissolved oxygen in the artificial wetland system is increased, which is conducive to the nitrification reaction of ammonia nitrogen; on the other hand, ammonia nitrogen is precipitated, which further realizes the removal of ammonia nitrogen;

[0021] 2. The system of the present invention realizes the deep removal of nitrate nitrogen in water. In the process, nitrate nitrogen undergoes denitrification reaction under anoxic conditions by means of reflux, thus realizing the process of deep denitrification;

[0022] 3. The present invention realizes enhanced removal of nitrogen and phosphorus during reoxygenation by planting eco-pond plants and enriching microalgae in the eco-pond, and greatly reduces investment and maintenance costs, thus having broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the process flow of the present invention;

[0024] Figure 2 It is a schematic diagram of the structure of the first-level artificial wetland of the present invention;

[0025] Figure 3 It is a schematic diagram of the structure of the second-level ecological pond of the present invention;

[0026] Figure 4 This is a schematic diagram of the top view of the second-level ecological pond of the present invention;

[0027] Figure 5 It is a schematic diagram of the structure of the third-level artificial wetland of the present invention.

[0028] The names corresponding to the marks in the figure are:

[0029] 1. First-level artificial wetland; 11. First baffle; 12. Second baffle; 13. First gravel layer; 14. First matrix layer; 2. Second-level ecological pond; 21. Third baffle; 22. Fourth baffle; 23. Second gravel layer; 24. Non-woven fabric; 25. Fixing rope; 26. Float valve; 3. Third-level artificial wetland; 31. Fifth baffle; 32. Sixth baffle; 33. Third gravel layer; 34. Second matrix layer; 4. Return pipe. DETAILED DESCRIPTION

[0030] The technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0031] Process implementation:

[0032] like Figure 1-5 As shown, the present invention includes a first-level artificial wetland, a second-level ecological pond and a third-level artificial wetland connected in sequence, wherein the artificial wetlands are all horizontal submerged flow type; the effective area ratio of the three-level treatment unit is 1: (0.5-1): (0.5-1), and the water level is controlled at 0-10 cm below the first and third-level artificial wetland matrix layers.

[0033] The first baffle and the second baffle are respectively arranged on the water inlet side and the water outlet side of the first artificial wetland. Both the first baffle and the second baffle are baffles with holes. Water enters from the middle of the water inlet side of the first artificial wetland and flows out from the upper part of the water outlet side. The first gravel layer and the first matrix layer are arranged from bottom to top in sequence between the first baffle and the second baffle. The particle size of the gravel in the first gravel layer is 2-3 cm. The first matrix layer is a uniform mixture of volcanic rock, magnesite and zeolite with a particle size of 1-2 cm. The volume ratio of volcanic rock, magnesite and zeolite is 1:1:1. Wetland plants are planted in the first artificial wetland, including yellow iris, iris, reed, canna, etc., with a density of 90-110 plants / m 2 , the plant roots are rooted in the first substrate layer.

[0034] The effluent from the first-level artificial wetland falls into the second-level ecological pond. A third baffle and a fourth baffle are respectively arranged on the inlet side and the outlet side of the second-level ecological pond, wherein the third baffle is a baffle with holes and the fourth baffle is a baffle without holes. A second gravel layer is arranged at the bottom of the second-level ecological pond, and the second gravel layer is located behind the inlet side of the third baffle. At the same time, the second gravel layer passes through the fourth baffle, and the fourth baffle is located above the second gravel layer. The particle size of the gravel in the second gravel layer is 2 to 3 cm. A layer of 1 mm thick non-woven fabric and a float valve are fixed above the second-level ecological pond by a fixed rope. Microalgae are enriched through the non-woven fabric, and ecological pond plants are planted through the float valve, including plants with narrow leaves such as cattail, iris, and calamus, with a density of 40 to 50 plants / m 2 , the plants are fixed in the raft, and their roots pass through the non-woven fabric and are immersed in the water.

[0035] The outflow of the second ecological pond flows back to the front end of the first artificial wetland through the return pipe, and the other part falls into the third artificial wetland. The fifth baffle and the sixth baffle are respectively arranged on the water inlet and outlet sides of the third artificial wetland, and the third gravel layer and the second matrix layer are arranged from bottom to top between the fifth baffle and the sixth baffle; the fifth baffle is a perforated baffle, the sixth baffle corresponding to the third gravel layer is a perforated baffle, and the baffle corresponding to the second matrix layer is a non-perforated baffle; the particle size of the gravel in the third gravel layer is 2-3 cm, and the second matrix layer is a uniform mixture of volcanic rock and zeolite, wherein the volume ratio of volcanic rock to zeolite is 1:1, and the particle size of volcanic rock and zeolite is 1-2 cm; wetland plants are planted in the third artificial wetland, including yellow calamus, iris, reed, canna, etc., with a density of 90-110 plants / m 2 , the plant roots are rooted in the second substrate layer.

[0036] Principle of the invention:

[0037] Gravel has a strong adsorption performance for nitrate nitrogen and phosphorus, but its biocompatibility is poor, and it is suitable as a supporting layer; zeolite has a better performance only in the adsorption of ammonia nitrogen, volcanic rock has a better effect in the adsorption of nitrate nitrogen and phosphorus, and magnesite can provide magnesium ions; therefore, in the first-level artificial wetland of the present invention, gravel is used as a supporting layer, and a mixture of volcanic rock, zeolite and magnesite is used as a matrix. During the process, on the one hand, ammonia nitrogen and phosphorus can be adsorbed, and on the other hand, inorganic phosphorus and ammonia nitrogen can be precipitated to obtain struvite, which realizes the solidification of nitrogen and phosphorus, and also helps the utilization of plants, thereby improving the removal efficiency of nitrogen and phosphorus.

[0038] In the second-level ecological pond, the water body is reoxygenated by microalgae, causing the residual ammonia nitrogen in the water body to undergo nitrification reaction to obtain nitrate nitrogen. At the same time, the phosphorus in the water body is also used by microorganisms and plants. A portion of the nitrate nitrogen in the effluent is returned to the first-level artificial wetland through reflux. In the first-level artificial wetland, due to the presence of volcanic rocks, under the action of sulfur autotrophic denitrifying bacteria, the nitrate nitrogen undergoes denitrification reaction to produce nitrogen gas, thus realizing the denitrification process.

[0039] The effluent from the second-level ecological pond enters the third-level artificial wetland, where the residual nitrogen and phosphorus are further removed through adsorption and denitrification reactions, thereby achieving the overall process of nitrogen and phosphorus removal.

[0040] How to run:

[0041] Start-up: Mix the sludge from the anoxic tank of the sewage treatment plant with the influent water and let it enter the cascade combination system with the influent water for microbial inoculation.

[0042] The system was initially started up using artificially simulated sewage with a carbon:nitrogen:phosphorus ratio of 100:20:1 as the influent. The hydraulic retention time was set to 24-48 hours, the reflux ratio was 100-200%, and it ran continuously for 15-20 days. The system effluent was stable, and the microalgae biofilm was clearly enriched on the non-woven fabric of the ecological pond, which indicated that the system startup was complete.

[0043] Operation: Sewage with a low carbon-nitrogen ratio (10:3) enters the system from the first-stage artificial wetland. After being treated in the first-stage artificial wetland, the second-stage ecological pond and the third-stage artificial wetland, various forms of nitrogen and phosphorus in the water body are enhanced and removed, and then discharged into the natural water body.

[0044] Example 1

[0045] A multi-level artificial wetland-ecological pond combined pilot system was constructed, which mainly consisted of a first-level artificial wetland, a second-level ecological pond and a third-level artificial wetland; among them, the first and third-level artificial wetlands were 110 cm long, 40 cm wide and 60 cm deep, and the second-level ecological pond was 110 cm long, 40 cm wide and 60 cm deep; the area ratio of the three-level treatment units was 1:1:1.

[0046] For the first-level artificial wetland, a first gravel layer with a depth of 20 cm and a diameter of 2 to 3 cm is laid at the bottom, and a 40 cm deep mixed matrix of volcanic rock (particle size 1 to 2 cm), zeolite (particle size 1 to 2 cm) and dolomite (particle size 1 to 2 cm) is laid on the first gravel layer (mixed in a volume ratio of 1:1:1); for the second-level ecological pond, a second gravel layer with a depth of 20 cm and a particle size of 2 to 3 cm is laid at the bottom; for the third-level artificial wetland, a third gravel layer with a depth of 20 cm and a diameter of 2 to 3 cm is laid at the bottom, and a 40 cm deep mixed matrix of volcanic rock (particle size 1 to 2 cm) and zeolite (particle size 1 to 2 cm) is laid on the third gravel layer (mixed in a volume ratio of 1:1).

[0047] Iris pumila was planted in the first and third level artificial wetlands, with a planting density of 100 plants / m 2 In the second-level ecological pond, cattails are planted in floating rafts with a planting density of 40 plants / m 2 A layer of 1mm thick non-woven fabric is laid flat under the raft, and the plant roots pass through the non-woven fabric and are immersed in the water.

[0048] Startup: The sludge from the anoxic tank of the sewage treatment plant is mixed with the influent and enters the cascade combination system with the influent for microbial inoculation. The artificially configured simulated sewage with carbon: nitrogen: phosphorus = 100:20:1 is used as the influent for initial startup. The water quality is COD = 100mg / L, TN = 20mg / L, TP = 1mg / L, the water level is controlled 10cm below the first and third artificial wetland matrix layers, the hydraulic retention time is set to 24h, and the reflow ratio is 150%. After 15 days of continuous operation, the system effluent is stable, and the microalgae biofilm that is obviously enriched on the non-woven fabric of the ecological pond is visible to the naked eye, and the system startup is considered complete.

[0049] Operation: With simulated sewage inlet of chemical oxygen demand = 50mg / L, ammonia nitrogen = 5mg / L, nitrate nitrogen = 10mg / L and total phosphorus = 0.5mg / L, the sewage enters the system from the first-stage artificial wetland and is discharged into natural water bodies after a series of treatments.

[0050] Embodiment effect:

[0051] During the operation of the system, the dissolved oxygen in the effluent of the first-stage artificial wetland was maintained at 0.42 mg / L, which was anoxic, while the dissolved oxygen in the effluent of the second-stage ecological pond was maintained at 2.4 mg / L, and the dissolved oxygen in the effluent of the third-stage artificial wetland dropped to 0.33 mg / L, which was anoxic. The above results show that the horizontal subsurface flow artificial wetland has serious oxygen consumption, and the dissolved oxygen has been significantly improved through the reoxygenation process of microalgae in the second-stage ecological pond, which is conducive to the oxygen consumption process of the second-stage ecological pond and its subsequent treatment process.

[0052] In the final effluent of the third-level artificial wetland, the removal rates of ammonia nitrogen, nitrate nitrogen, total nitrogen, COD and total phosphorus reached 98.8%, 99.2%, 99.0%, 93.52% and 94.0% respectively, and the effluent concentrations were 0.06mg / L, 0.08mg / L, 0.15mg / L, 3.24mg / L and 0.03mg / L respectively, achieving the simultaneous enhanced removal of various forms of nitrogen, phosphorus and organic matter.

[0053] The present invention is not limited to the above-mentioned optimal implementation mode. Anyone can derive other various forms of products under the inspiration of the present invention. However, no matter what changes are made in the shape or structure, all technical solutions that are the same or similar to those of the present application fall within the protection scope of the present invention.

Claims

1. A cascade artificial wetland system for natural reoxygenation to enhance denitrification and phosphorus removal, characterized by: It includes the first-level artificial wetland, the second-level ecological pond and the third-level artificial wetland connected in sequence; Wetland plants are planted in the first-level artificial wetland and the third-level artificial wetland, and ecological pond plants are planted in the second-level ecological pond; The first-stage artificial wetland is provided with a first gravel layer and a first matrix layer, and the first matrix layer is a mixture of volcanic rock, zeolite and magnesite; The second-level ecological pond is provided with a second gravel layer, a non-woven fabric and a float valve are fixed above the second-level ecological pond, microalgae are enriched on the non-woven fabric, and ecological pond plants are planted on the float valve; The third-level artificial wetland is provided with a third gravel layer and a second matrix layer, and the second matrix layer is a mixture of volcanic rock and zeolite; The outflow of the second-stage ecological pond flows back to the front end of the first-stage artificial wetland.

2. The cascade artificial wetland system for natural reoxygenation and enhanced denitrification and phosphorus removal according to claim 1, characterized in that: The area ratio of the first-level artificial wetland, the second-level ecological pond and the third-level artificial wetland is 1:0.5~1:0.5~1; in the first-level artificial wetland and the third-level artificial wetland, the water level is controlled at 0~10cm below the substrate layer; the hydraulic retention time is 24~48h; the return ratio of the second-level ecological pond effluent return is 100~200%.

3. The cascade artificial wetland system for natural reoxygenation and enhanced denitrification and phosphorus removal according to claim 1, characterized in that: The particle sizes of gravel in the first gravel layer, the second gravel layer and the third gravel layer are all 2-3 cm; the particle sizes of volcanic rock, zeolite and magnesite in the first matrix layer are all 1-2 cm, and the volume ratio of volcanic rock, zeolite and magnesite is 1:1:1; the particle sizes of volcanic rock and zeolite in the second matrix layer are all 1-2 cm, and the volume ratio of volcanic rock to zeolite is 1:

1.

4. The cascade artificial wetland system for natural reoxygenation and enhanced denitrification and phosphorus removal according to claim 1, characterized in that: The wetland plants are rooted in the matrix layer. The wetland plants include yellow iris, iris, reed and canna, with a planting density of 90 to 110 plants / m 2 .

5. The cascade artificial wetland system for natural reoxygenation and enhanced denitrification and phosphorus removal according to claim 1, characterized in that: The roots of the eco-pond plants are rooted in the water through the non-woven fabric. The eco-pond plants include cattail, iris and calamus, with a planting density of 40 plants / m 2 .

6. The cascade artificial wetland system for natural reoxygenation and enhanced denitrification and phosphorus removal according to claim 1, characterized in that: The first-level artificial wetland is provided with a first baffle and a second baffle on the water inlet side and the water outlet side, respectively, the first gravel layer and the first matrix layer are located between the first baffle and the second baffle, and the first baffle and the second baffle are baffles with holes; a third baffle and a fourth baffle are provided on the water inlet side and the water outlet side of the second-level ecological pond, respectively, the second gravel layer is located behind the water inlet side of the third baffle, the fourth baffle is located above the second gravel layer, the third baffle is a baffle with holes, and the fourth baffle is a baffle without holes; a fifth baffle and a sixth baffle are provided on the water inlet side and the water outlet side of the third-level artificial wetland, respectively, the third gravel layer and the second matrix layer are located between the fifth baffle and the sixth baffle, the fifth baffle is a baffle with holes, the lower side of the sixth baffle is a baffle with holes, and the upper side is a baffle without holes, and the height of the baffle with holes on the lower side of the sixth baffle is consistent with the height of the third gravel layer.

7. The cascade artificial wetland system for natural reoxygenation and enhanced denitrification and phosphorus removal according to claim 6, characterized in that: The water inlet of the first-level artificial wetland is located in the middle of the water inlet side, and the water outlet is located above the water outlet side, and the water outlet falls into the second-level ecological pond; the water inlet of the second-level ecological pond is located above the water inlet side, and the water outlet is located above the water outlet side, and the water outlet falls into the third-level artificial wetland; the water inlet of the third-level artificial wetland is located above the water inlet side, and the water outlet is located above the water outlet side.

8. A cascade artificial wetland system for natural reoxygenation and enhanced denitrification and phosphorus removal according to any one of claims 1 to 7, characterized in that: The artificial wetland system has an ammonia nitrogen removal rate of up to 98.8%, a nitrate nitrogen removal rate of up to 99.2%, a total nitrogen removal rate of up to 99.0%, a COD removal rate of up to 93.52%, and a total phosphorus removal rate of up to 94.0%.

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