A biochar enhanced composite constructed wetland nitrogen and phosphorus removal system

Abstract

The present invention discloses a biochar enhanced composite artificial wetland denitrification and phosphorus removal system, including an artificial wetland, an insulation layer is arranged outside the pool body, and the artificial wetland is provided with at least seven layers from bottom to top, which are: a sedimentation zone, a first zeolite layer, an aerobic anaerobic layer, a second zeolite layer, an aerobic layer, a mixed matrix layer and a soil layer; a heating device is installed between the sedimentation zone and the first zeolite layer; the aerobic anaerobic layer is divided into three areas by a partition, namely, an aerobic zone, an anaerobic zone and an outlet zone, and the aerobic zone and the anaerobic zone are respectively filled with aerobic microbial fillers and anaerobic zone microbial fillers; an aeration device is arranged at the bottom of the aerobic zone. In view of the problems of poor reoxygenation effect, low removal rate of nitrogen, phosphorus and COD, easy clogging and great influence of temperature in the current vertical flow artificial wetland, the present invention provides a sludge biochar enhanced composite artificial wetland denitrification and phosphorus removal system with high reoxygenation capacity, good denitrification and phosphorus removal effect, small footprint and low temperature operation.

Description

Technical Field

[0001] The invention relates to the technical field of artificial wetlands, and in particular to a biochar-enhanced composite artificial wetland denitrification and phosphorus removal system. Background Art

[0002] Artificial wetlands are a type of sewage treatment technology that simulates natural wetlands to purify pollutants. They are mainly composed of artificial substrates, microorganisms and aquatic plants, and purify sewage through the synergistic effects of physics, chemistry and biology. The artificial substrate can provide a stable attachment surface for the growth of microorganisms, provide carriers and nutrients for aquatic plants, and can also adsorb some pollutants; aquatic plants can directly absorb and utilize nutrients in sewage, enrich some toxic and harmful substances, and can also transport oxygen to the root zone to maintain hydraulic transmission; microorganisms degrade organic pollutants in sewage through their own metabolism. Artificial wetlands have the advantages of low investment, convenient management, stable treatment effect and beautification of the environment, and have broad application prospects. At present, they have been widely used in sewage plant tailwater treatment, domestic sewage, river pollution and storm runoff and other pollution fields.

[0003] Fillers are an important component of artificial wetlands. They can not only carry microorganisms, but also remove pollutants through physical and chemical adsorption. Wetland fillers are mainly divided into natural materials such as soil, gravel, zeolite, limestone, industrial by-products such as ash, blast furnace slag, fly ash, and artificial products such as ceramsite, ceramsite filter material, and plastic. The type, pore size, specific surface area, carbon content, and filling method of the filler will affect the reoxygenation capacity of the wetland, the type and activity of microorganisms. Reasonable selection of filler types and filling methods is conducive to improving the reoxygenation capacity of the wetland and the removal effect of pollutants.

[0004] However, artificial wetlands still have the following problems: (1) The oxygen supply capacity of artificial wetlands is insufficient, and the oxygen mass transfer rate of the filler is low, which limits the nitrification capacity of microorganisms and leads to poor removal of ammonia nitrogen. (2) Artificial wetlands mainly rely on the adsorption of microorganisms and pollutants by fillers to purify organic matter and nitrogen and phosphorus in sewage. However, the adsorption of microorganisms and pollutants by traditional fillers is small, resulting in limited effect of microorganisms in purifying sewage and poor removal of nitrogen, phosphorus and COD in sewage. (3) The hydraulic retention time of artificial wetlands is long, and the amount of microorganisms loaded on the fillers is small, resulting in a large amount of free microorganisms in the wetland, which can easily lead to wetland blockage. (4) Plants and microorganisms in artificial wetlands are greatly affected by temperature. Cold weather can affect the activity of microorganisms and reduce the wetland's treatment effect on wastewater.

[0005] To this end, we proposed a biochar-enhanced composite artificial wetland denitrification and phosphorus removal system to solve the above problems. Summary of the invention

[0006] The object of the present invention is to provide a biochar enhanced composite artificial wetland denitrification and phosphorus removal system to solve the problems raised in the above background technology.

[0007] To achieve the above object, the present invention provides the following technical solution: a biochar enhanced composite artificial wetland denitrification and phosphorus removal system, comprising an artificial wetland, the artificial wetland is constructed with a reinforced concrete structure, an anti-seepage layer is arranged on the inner side wall and the bottom surface of the artificial wetland pool, and an insulation layer is arranged on the outside of the pool, and the artificial wetland is provided with at least seven layers from bottom to top, which are: a sedimentation area, a first zeolite layer, an aerobic anaerobic layer, a second zeolite layer, an aerobic layer, a mixed matrix layer and a soil layer;

[0008] A heating device is installed between the precipitation zone and the first zeolite layer;

[0009] The aerobic and anaerobic layer is divided into three areas by a partition, namely an aerobic area, an anaerobic area and an outlet area, and the aerobic area and the anaerobic area are filled with aerobic microbial fillers and anaerobic area microbial fillers respectively;

[0010] An aeration device is arranged at the bottom of the aerobic zone.

[0011] Preferably, a water inlet pipeline is distributed in the sedimentation area, and a plurality of water outlet holes are evenly opened at the lower end of the water inlet pipeline.

[0012] Preferably, a three-phase separator is provided above the sedimentation zone, a funnel-shaped sewage collection zone is provided below the sedimentation zone, and a sludge discharge port connected to the outside of the artificial wetland is provided at the outer end of the sewage collection zone.

[0013] Preferably, the heating device is composed of a heating resistor and a temperature control device. The heating resistor is evenly distributed between the precipitation zone and the first zeolite layer and is electrically connected to the temperature control device. The temperature control device is powered by an external power supply.

[0014] Preferably, the first zeolite layer and the second zeolite layer are both filled with zeolite, wherein: the zeolite particle size of the first zeolite layer is 16-32 mm, and the height of the first zeolite layer is 25-35 cm;

[0015] The zeolite particle size of the second zeolite layer is 8-16 mm, and the height of the second zeolite layer is 20-30 cm.

[0016] Preferably, the aerobic microbial filler is a soft filler composed of a PE central rope and polyester yarn;

[0017] The anaerobic zone microbial filler is a porous plastic hollow ball filler, including a porous large hollow ball and a porous small hollow ball. The small hollow ball is suspended inside the large hollow ball and connected to the large hollow ball by elastic fiber winding. A plurality of porous expanded clay particles are arranged inside the small hollow ball.

[0018] Preferably, a stainless steel wire mesh is arranged between the aerobic zone and the first zeolite layer and fixed by bolts, and the pore size of the stainless steel wire mesh is less than 3 mm;

[0019] A partition is also arranged between the anaerobic zone and the effluent zone and the first zeolite layer, and the height of the aerobic anaerobic layer is 35cm-40cm.

[0020] Preferably, the aeration device is composed of an aeration pipe and an aeration head, a plurality of aeration heads are evenly distributed on the aeration pipe, the aeration pipe passes through the pool wall of the artificial wetland, and is connected to an air compressor, and the air compressor is powered by an external power supply.

[0021] Preferably, the mixed matrix layer is a mixture of zeolite and sludge biochar in a volume ratio of 1:1, with a particle size of 3-5 mm; the sludge biochar is obtained by high-temperature anoxic carbonization of sludge, with a carbonization temperature of 500°C and a carbonization time of 2 hours. A stainless steel wire mesh is also provided between the mixed matrix layer and the aerobic layer, and the height of the mixed matrix layer is 20-30 cm.

[0022] Preferably, wetland plants are planted on the soil layer, and the wetland plants are plants commonly used in the art, such as canna; a water outlet is opened on one side of the soil layer, and the water outlet passes through the upper end of the artificial wetland pool wall.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] In view of the problems of poor reoxygenation effect, low nitrogen, phosphorus and COD removal rates, easy clogging and great temperature influence in the current vertical flow artificial wetlands, the present invention provides a sludge biochar enhanced composite artificial wetland denitrification and phosphorus removal system with high reoxygenation capacity, good denitrification and phosphorus removal effects, small footprint and low-temperature operation.

[0025] The present invention combines sludge biochar with traditional fillers as artificial wetland fillers, and utilizes the porous structure, large porosity and specific surface area, and abundant functional groups of biochar to improve the adsorption effect of wetland fillers on pollutants such as organic matter and phosphorus;

[0026] The present invention combines the MBBR process with an artificial wetland to increase the fixation of microorganisms in the artificial wetland and improve the denitrification effect of the wetland; the oxygen content of the wetland is supplemented by aeration to solve the problems of insufficient oxygen in the artificial wetland and the great influence of temperature.

[0027] The present invention provides a heating resistance wire to reduce the problem that microorganisms in artificial wetlands are greatly affected by temperature, thereby improving the sewage treatment effect of artificial wetlands under low temperature conditions in winter. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram of the structure of the present invention;

[0029] Figure 2 This is a schematic diagram of the structure of the anaerobic zone microbial filler in the present invention;

[0030] Figure 3 This is a diagram showing the removal effect of artificial wetlands on actual domestic sewage TP in the present invention;

[0031] Figure 4 This is a diagram showing the removal effect of artificial wetlands on actual domestic sewage TN in the present invention;

[0032] Figure 5 This is a diagram showing the effect of artificial wetlands in the present invention on the removal of ammonia nitrogen from actual domestic sewage;

[0033] Figure 6 This is a diagram showing the removal effect of COD in actual domestic sewage by the artificial wetland of the present invention;

[0034] In the figure: 1, artificial wetland; 101, insulation layer; 11, sedimentation zone; 12, first zeolite layer; 13, aerobic anaerobic layer; 131, aerobic zone; 131a, aerobic microbial filler; 132, anaerobic zone; 132a, anaerobic zone microbial filler; 133, effluent zone; 134, partition; 13-a, large hollow ball; 13-b, elastic fiber; 13-c, small hollow ball; 13-d, porous ceramsite; 14, second zeolite layer; 15, aerobic layer ; 16. Mixed matrix layer; 17. Soil layer; 171. Water outlet; 2. Water inlet pipe; 201. Water outlet; 3. Three-phase separator; 4. Sewage collection area; 401. Sludge discharge port; 5. Heating device; 51. Heating resistor wire; 52. Temperature control device; 53. Generator; 54. Battery; 55. Solar panel; 6. Stainless steel wire mesh; 7. Aeration device; 71. Aeration pipe; 72. Aeration head; 73. Air compressor; 8. Wetland plants. DETAILED DESCRIPTION

[0035] The technical solution of the present invention will be described below in conjunction with the accompanying drawings and embodiments.

[0036] See also Figure 1-2 The present invention provides a technical solution: a biochar enhanced composite artificial wetland denitrification and phosphorus removal system, including an artificial wetland 1, the artificial wetland 1 is constructed with a reinforced concrete structure, the inner side wall and bottom surface of the artificial wetland 1 are provided with an anti-seepage layer, and the outer side of the artificial wetland 1 is provided with an insulation layer 101, the insulation layer 101 can maintain the temperature of the sewage in the pool and improve the activity of microorganisms in the pool under low temperature conditions. It is characterized in that: the artificial wetland 1 is provided with at least seven layers from bottom to top, which are: a sedimentation area 11, a first zeolite layer 12, an aerobic anaerobic layer 13, a second zeolite layer 14, an aerobic layer 15, a mixed matrix layer 16 and a soil layer 17;

[0037] In one embodiment of the present invention, a water inlet pipe 2 is distributed in the sedimentation area 11, and a plurality of water outlet holes 201 are evenly opened at the lower end of the water inlet pipe 2; a three-phase separator 3 is also arranged above the sedimentation area 11, a funnel-shaped sewage collection area 4 is arranged below the sedimentation area 11, and a sludge discharge port 401 connected to the outside of the artificial wetland 1 is arranged at the outer end of the sewage collection area 4; the setting of the sedimentation area 11 is conducive to the sedimentation of suspended solids and aged microorganisms and their extracellular polymers, thereby alleviating the clogging problem of the artificial wetland.

[0038] A heating device 5 is installed between the precipitation zone 11 and the first zeolite layer 12 .

[0039] In one embodiment of the present invention, the heating device 5 is composed of a heating resistor 51 and a temperature control device 52. The heating resistor 51 is evenly distributed between the precipitation area 11 and the first zeolite layer 12, and is electrically connected to the temperature control device 52. The temperature control device 52 is powered by an external power supply. The external power supply in the present invention can be powered by a generator 53, a battery 54 or a solar panel 55. The sewage will be heated when it flows through the heating resistor 51, which increases the temperature of the sewage in the artificial wetland pool, which is beneficial to maintaining the activity of microorganisms in the artificial wetland, so that the artificial wetland can operate normally in a low temperature environment in winter. The heating device operates at low temperatures and is idle when the temperature is high.

[0040] The first zeolite layer 12 and the second zeolite layer 14 are both filled with zeolite, wherein: the zeolite particle size of the first zeolite layer 12 is 16-32 mm, and the height of the first zeolite layer 12 is 25-35 cm; the zeolite particle size of the second zeolite layer 14 is 8-16 mm, and the height of the second zeolite layer is 20-30 cm.

[0041] The aerobic-anaerobic layer 13 is divided into three areas by a partition 133, namely an aerobic area 131, an anaerobic area 132 and an outlet area 133. The aerobic area 131 and the anaerobic area 132 are filled with aerobic microbial fillers 131a and anaerobic area microbial fillers 132a respectively.

[0042] The aerobic microbial filler 131a is a soft filler composed of a PE central rope and polyester yarn;

[0043] The anaerobic zone microbial filler 132a is a porous plastic hollow ball filler, including a porous large hollow ball 13-a and a porous small hollow ball 13-c, the small hollow ball 13-c is suspended inside the large hollow ball 13-a, and is connected to the large hollow ball 13-a by winding with elastic fibers 13-b, and a plurality of porous ceramsite 13-d are arranged inside the small hollow ball 13-c. The high dissolved oxygen content of sewage passing through the aerobic zone will lead to an incomplete anaerobic environment in the anaerobic zone, and this anaerobic filler can make the microorganisms hanging on the elastic fibers deplete oxygen, so that the microorganisms hanging on the porous ceramsite are in an absolutely anaerobic environment.

[0044] In addition, a stainless steel wire mesh 6 is provided between the aerobic zone 131 and the first zeolite layer 12 and fixed by bolts, and the aperture of the stainless steel wire mesh 6 is less than 3 mm;

[0045] A partition 134 is also provided between the anaerobic zone 132 and the effluent zone 133 and the first zeolite layer 12. The height of the aerobic anaerobic layer 13 is 35 cm to 40 cm.

[0046] An aeration device 7 is provided at the bottom of the aerobic zone 131 .

[0047] In one embodiment of the present invention, the aeration device 7 is composed of an aeration pipe 71 and an aeration head 72. A plurality of aeration heads 72 are evenly distributed on the aeration pipe 71. The aeration pipe 71 passes through the pool wall of the artificial wetland 1 and is connected to an air compressor 73. The air compressor 73 is powered by an external power supply. The external power supply can be the same power supply as the temperature control device, and can be powered by a generator 53, a battery 54, or a solar panel 55. The aeration device 7 can provide oxygen for the growth and metabolism of microorganisms in the aerobic zone 131.

[0048] Furthermore, the mixed matrix layer 16 is made of zeolite and sludge biochar mixed in a volume ratio of 1:1, with a particle size of 3-5 mm; the sludge biochar is obtained by high-temperature anoxic carbonization of sludge, the carbonization temperature is 500°C, and the carbonization time is 2 hours. The addition of sludge biochar can improve the removal effect of artificial wetlands on phosphorus in sewage. A stainless steel wire mesh 6 is also arranged between the mixed matrix layer 16 and the aerobic layer 131, and the height of the mixed matrix layer 16 is 20-30 cm.

[0049] Furthermore, wetland plants 8 are planted on the soil layer 17 , and the wetland plants 8 are plants commonly used in the art, such as canna. A water outlet 171 is opened on one side of the soil layer 17 , and the water outlet 171 passes through the upper end of the pool wall of the artificial wetland 1 .

[0050] In order to verify the strengthening effect of sludge biochar on artificial wetlands, three groups of artificial wetlands were set up. The artificial wetland pools were 10 cm long, 10 cm wide and 20 cm high. The first group was set as a zeolite group, and zeolites were filled in sequence from bottom to top, where the first zeolite layer was 4.5 cm, the second zeolite layer was 5 cm, and the third zeolite layer was 5 cm. The second group was set as a zeolite: biochar = 2:1 group, which was the first zeolite layer, the second zeolite layer and the mixed matrix layer from bottom to top. The mixed matrix layer was filled with zeolite and biochar in a volume ratio of 2:1, where the first zeolite layer was 4.5 cm, the second zeolite layer was 5 cm , the mixed matrix layer is 5cm; the third group is set as zeolite: biochar = 1:1 group, from bottom to top are the first zeolite layer, the second zeolite layer and the mixed matrix layer, the mixed matrix layer is filled with zeolite and biochar in a volume ratio of 1:1, of which the first zeolite layer is 4.5cm, the second zeolite layer is 5cm, and the mixed matrix layer is 5cm; an intermittent water inlet method is adopted, the water inlet pump runs for 3h and stops for 3h, runs 4 times a day, the water inlet flow rate is 0.28-0.42mL / min, the operating hydraulic retention time HRT is 2-3 days, and the operating time is from mid-September to mid-November.

[0051] Attached Figure 3-6 This is a diagram showing the removal effects of three groups of artificial wetlands on TP, TN, ammonia nitrogen and COD in actual domestic sewage.

[0052] The following table shows the average experimental data of three groups of artificial wetlands for sewage treatment when HRT = 3d:

[0053] From the table below, we can find that: comparing the three groups of artificial wetlands, the artificial wetland with a 1:1 volume mixture of biochar and zeolite has the best effluent quality, reaching the Class A emission standard of "Pollutant Discharge Standard for Urban Wastewater Treatment Plants" (GB18918-2002), with a removal rate of TP and COD exceeding 80%, ammonia nitrogen exceeding 70%, and TN exceeding 50%. In addition, the effluent quality of the artificial wetland with biochar added is better than that of the group without biochar added, which shows that biochar has a good adsorption effect on TP, and can also increase the nitrification and denitrification of the wetland, and improve the denitrification effect of the artificial wetland. Therefore, biochar has a good strengthening effect on the denitrification and phosphorus removal of artificial wetlands.

[0054] The following table shows the average values ​​of experimental data obtained from three groups of artificial wetlands for sewage treatment during the stable operation stage of HRT = 3d:

[0055]

[0056] The biochar added in the present invention is obtained by carbonizing the sludge waste generated in the secondary sedimentation tank of the sewage treatment plant, which is recycled back into sewage treatment, playing the role of treating waste with waste. Compared with traditional wetland fillers, sludge biochar has better adsorption performance for phosphorus, and improves the adsorption effect of the filler matrix in the wetland on pollutants. The specific steps are as follows:

[0057] Sewage flows in from the bottom of the artificial wetland pool 1 . When the sewage flows through the first zeolite layer 12 , large suspended matter in the sewage is filtered and retained, and the retained suspended matter settles in the sedimentation area 11 .

[0058] When the sewage flows through the aerobic zone 131, the hydraulic force fully contacts the aerobic microbial filler 131a from bottom to top. In the aerated environment, the aerobic microorganisms carry out nitrification, consume part of the organic matter, and convert the ammonia nitrogen in the sewage into nitrate nitrogen. When passing through the anaerobic zone, the anaerobic microorganisms use the COD in the sewage as a carbon source to carry out denitrification, convert the nitrate nitrogen produced in the aerobic zone into N2 for release, and effectively improve the denitrification effect of the artificial wetland.

[0059] At the same time, the phosphate-releasing bacteria release a large amount of phosphorus in the anaerobic environment, and then enter the second zeolite layer 14 for filtration. The filtered sewage then enters the aerobic layer 15, and the phosphorus released by the phosphate-releasing bacteria in the anaerobic zone 132 is absorbed by the polyphosphate bacteria in the aerobic layer 15. Then, it enters the mixed matrix layer 16, and utilizes the good adsorption effect of phosphate by sludge biochar to better enhance the phosphorus removal effect of the artificial wetland. Finally, it enters the soil layer 17, and utilizes the plant root system to further purify the sewage, and the purified sewage is discharged from the outlet.

[0060] The suspended solids, aged microorganisms and their extracellular polymers in the sewage are settled in the sedimentation zone 11 through the three-phase separator 3 and then discharged from the sludge discharge port 401.

[0061] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A biochar enhanced composite artificial wetland denitrification and phosphorus removal system, comprising an artificial wetland, an insulation layer is arranged outside the pool, and is characterized by: The artificial wetland is provided with at least seven layers from bottom to top, which are: a sedimentation area, a first zeolite layer, an aerobic anaerobic layer, a second zeolite layer, an aerobic layer, a mixed matrix layer and a soil layer; A heating device is installed between the precipitation zone and the first zeolite layer; The aerobic and anaerobic layer is divided into three areas by a partition, namely, an aerobic area, an anaerobic area and a water outlet area. The aerobic area and the anaerobic area are filled with aerobic microbial fillers and anaerobic area microbial fillers respectively; the aerobic microbial fillers are soft fillers composed of PE central ropes and polyester yarns; The microbial filler in the anaerobic zone is a porous plastic hollow ball filler, including a porous large hollow ball and a porous small hollow ball. The small hollow ball is suspended inside the large hollow ball and connected to the large hollow ball by winding with elastic fibers. A plurality of porous ceramsite particles are arranged inside the small hollow ball. An aeration device is arranged at the bottom of the aerobic zone.

2. The biochar enhanced composite constructed wetland denitrification and phosphorus removal system according to claim 1, characterized in that: A water inlet pipeline is distributed in the sedimentation area, and a plurality of water outlet holes are evenly opened at the lower end of the water inlet pipeline.

3. The biochar enhanced composite constructed wetland denitrification and phosphorus removal system according to claim 1, characterized in that: A three-phase separator is also arranged above the sedimentation area, a funnel-shaped sewage collection area is arranged below the sedimentation area, and a sludge discharge port connected to the outside of the artificial wetland is arranged at the outer end of the sewage collection area.

4. The biochar enhanced composite constructed wetland denitrification and phosphorus removal system according to claim 1, characterized in that: The heating device is composed of a heating resistance wire and a temperature control device. The heating resistance wire is evenly distributed between the precipitation area and the first zeolite layer and is electrically connected to the temperature control device. The temperature control device is powered by an external power supply.

5. The biochar enhanced composite constructed wetland denitrification and phosphorus removal system according to claim 1, characterized in that: The first zeolite layer and the second zeolite layer are both filled with zeolite, wherein: the zeolite particle size of the first zeolite layer is 16-32 mm, and the height of the first zeolite layer is 25-35 cm; The zeolite particle size of the second zeolite layer is 8-16 mm, and the height of the second zeolite layer is 20-30 cm.

6. The biochar enhanced composite constructed wetland denitrification and phosphorus removal system according to claim 1, characterized in that: A stainless steel wire mesh is arranged between the aerobic zone and the first zeolite layer, and the pore size of the stainless steel wire mesh is less than 3 mm; A partition is also arranged between the anaerobic zone and the effluent zone and the first zeolite layer, and the height of the aerobic anaerobic layer is 35cm-40cm.

7. The biochar enhanced composite constructed wetland denitrification and phosphorus removal system according to claim 1, characterized in that: The aeration device is composed of an aeration pipe and an aeration head. A plurality of aeration heads are evenly distributed on the aeration pipe. The aeration pipe passes through the pool wall of the artificial wetland and is connected to an air compressor. The air compressor is powered by an external power supply.

8. The biochar enhanced composite constructed wetland denitrification and phosphorus removal system according to claim 1, characterized in that: The mixed matrix layer is a mixture of zeolite and sludge biochar in a volume ratio of 1:1, with a particle size of 3-5 mm; a stainless steel wire mesh is also arranged between the mixed matrix layer and the aerobic layer, and the height of the mixed matrix layer is 20-30 cm.

9. The biochar enhanced composite constructed wetland denitrification and phosphorus removal system according to claim 1, characterized in that: Wetland plants are planted on the soil layer, and a water outlet is opened on one side of the soil layer. The water outlet runs through the upper end of the artificial wetland pool wall.

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