Composite vertical flow constructed wetland

Abstract

The invention discloses a composite vertical flow constructed wetland. The composite vertical flow constructed wetland comprises a glass porous cross-linking modified slow-release carbon source matrix filler layer, wherein a glass porous cross-linking modified slow-release carbon source matrix is prepared from a glass porous matrix loaded with nano zero-valent iron and an alkali-treated modified biological carbon material through a cross-linking reaction. The constructed wetland disclosed by the invention can efficiently remove nitrogen and phosphorus, can still stably operate in a low-temperature environment, is small in occupied area and low in cost, and can effectively solve the problem of urban sewage.

Description

Technical Field

[0001] The invention relates to a composite vertical flow artificial wetland, belonging to the technical field of water treatment. Background Art

[0002] At present, the secondary effluent or tail water of urban sewage treatment plants in my country still contains a large amount of nitrogen, phosphorus and other substances. Constructed wetlands are widely used in the treatment of secondary effluent or tail water of sewage treatment plants as a deep treatment technology for denitrification and phosphorus removal. Since the secondary effluent or tail water of sewage treatment plants has less organic matter content and a low carbon-nitrogen ratio, it affects the nitrification and denitrification of microorganisms, resulting in low denitrification and phosphorus removal effects. At the same time, the operation effect of artificial wetlands is not good in winter due to low temperatures. Therefore, it is of great significance to develop a stable and efficient constructed wetland to solve the problem of urban sewage. Summary of the invention

[0003] In view of the shortcomings of the prior art, the present invention aims to provide a composite vertical flow artificial wetland. The artificial wetland can efficiently remove nitrogen and phosphorus, can still operate stably in a low temperature environment, occupies a small area, is low in cost, and can effectively solve the problem of urban sewage.

[0004] In order to achieve the above technical objectives, the present invention provides a composite vertical flow artificial wetland, which comprises a glass porous cross-linked modified slow-release carbon source matrix filler layer, wherein the glass porous cross-linked modified slow-release carbon source matrix is ​​prepared by a cross-linking reaction between a glass porous matrix loaded with nano zero-valent iron and an alkali-treated modified biocarbon material.

[0005] The glass porous cross-linked modified slow-release carbon source matrix in the present invention can effectively control the release of the carbon source and has an excellent heat preservation effect. Among them, the micro-electrolysis of nano zero-valent iron can promote the release of aromatic protein substances and fulvic acid substances in the carbon source, promote the carbon release process of the solid carbon source, and also act as an inorganic electron donor and reducing agent to provide electrons for denitrifying bacteria to perform anaerobic respiration, reducing nitrate nitrogen to N2 or NO2 - , and also acts as a deoxidizer, which can ensure the anaerobic environment of biological denitrification in the packing layer and promote the enrichment of denitrifying microorganisms in the packing layer; the carbon release performance of the modified biocarbon material treated with alkali is enhanced, the carbon release rate is increased, and the nitrogen and phosphorus release amount is low. The modified slow-release carbon source acts as an organic electron donor to provide a carbon source for denitrifying bacteria. The glass porous cross-linked modified slow-release carbon source matrix of the present invention greatly improves the denitrification efficiency and stability of the artificial wetland system through the synergistic denitrification of the modified slow-release carbon source, nano zero-valent iron and glass porous materials. As a preferred scheme, the preparation process of the glass porous cross-linked modified slow-release carbon source matrix is: the alkali-treated modified biocarbon material and water are mixed and heated to gelatinize to obtain a gelatinized liquid; the gelatinized liquid is cross-linked with polyvinyl alcohol, a foaming agent and a glass porous matrix loaded with nano zero-valent iron, and then freeze-formed to obtain the product.

[0006] Among them, polyvinyl alcohol (PVA) has abundant hydroxyl (-OH) functional groups, which can form hydrogen bonds with biocarbon materials to form stable slow-release complexes. The present invention can adjust the release rate of the carbon source by controlling the molecular weight, cross-linking degree of polyvinyl alcohol (PVA) and the pore structure of the biocarbon material.

[0007] As a preferred solution, the molecular weight of the polyvinyl alcohol is 170,000 to 220,000.

[0008] As a preferred solution, the mass ratio of the alkali-treated modified biochar material and water is (1~3):10.

[0009] As a preferred embodiment, the mass ratio of the gelatinized liquid, polyvinyl alcohol, the glass porous matrix loaded with nano-zero-valent iron and the foaming agent is (40-50):(3-5):(40-50):(1-2).

[0010] As a preferred solution, the foaming agent is sodium bicarbonate.

[0011] As a preferred solution, the heating gelatinization conditions are: temperature of 40-70° C. and time of 1-3 h.

[0012] As a preferred solution, the conditions of the cross-linking reaction are: temperature of 100-140° C. and time of 1-1.5 h.

[0013] As a preferred solution, the freezing molding conditions are: temperature of -15 to -12°C and time of 1 to 1.5 hours.

[0014] As a preferred solution, the preparation process of the glass porous matrix loaded with nano zero-valent iron is as follows: glass waste, borax powder, sodium phosphate powder, kaolin, blast furnace dust and foaming agent are mixed and calcined to obtain the obtained product.

[0015] As a preferred solution, the mass fraction of the glass waste is 30-40 parts, the mass fraction of the borax powder is 1-2 parts, the mass fraction of the sodium phosphate powder is 1-2 parts, the mass fraction of the kaolin is 15-20 parts, the mass fraction of the blast furnace dust is 20-30 parts, and the mass fraction of the foaming agent is 1-2 parts.

[0016] Among them, blast furnace dust is mainly used as an iron source and a carbon source, which can be calcined and reduced to generate nano-zero-valent iron and loaded into a glass porous matrix.

[0017] As a preferred solution, the foaming agent comprises magnesium carbonate and calcium carbonate.

[0018] As a preferred solution, the particle size of the glass waste is -150 mesh to +200 mesh.

[0019] As a preferred solution, the particle size of the borax powder is -150 mesh to +200 mesh.

[0020] As a preferred solution, the particle size of the sodium phosphate powder is -150 mesh to +200 mesh.

[0021] As a preferred solution, the particle size of the kaolin is -150 mesh to +200 mesh.

[0022] As a preferred solution, the particle size of the blast furnace dust is -150 mesh to +200 mesh.

[0023] As a preferred solution, the particle size of the foaming agent is -600 mesh to +800 mesh.

[0024] As a preferred solution, the calcination process is: first heat to 400-450°C for preheating for 10-20 minutes, then continue to heat to 800-900°C for melting for 30-40 minutes, then continue to heat to 1000-1100°C for sintering for 20-40 minutes, then cool to 500-800°C, and then naturally cool to room temperature.

[0025] As a preferred solution, the heating rates of the preheating, melting and sintering processes are all 10-20°C / min.

[0026] As a preferred solution, the cooling rate of the cooling process is 20-30°C / min.

[0027] As a preferred solution, the alkali-treated modified biochar material is prepared by soaking the biochar material in a sodium hydroxide solution.

[0028] Among them, alkali treatment can reduce the degree of cross-linking and firmness of cellulose. The principle is to use OH- to destroy the chemical bonds between lignin, cellulose and hemicellulose, and can also destroy the chemical bonds of lignin itself and decompose most of the lignin. The biochar material treated with alkali has enhanced carbon release performance, increased carbon release rate, and low nitrogen and phosphorus release.

[0029] As a preferred solution, the biochar material is rice straw.

[0030] As a preferred solution, the length of the rice straw is 0.5-1 cm.

[0031] The mass concentration of the sodium hydroxide solution is 1.5-2%.

[0032] As a preferred solution, the immersion temperature is 90-100° C. and the immersion time is 3-5 hours.

[0033] As a preferred solution, the composite vertical flow artificial wetland is divided into a downstream pool and an upstream pool, and the fillers in the downstream pool and the upstream pool include a bottom gravel filler layer, a glass porous cross-linked modified slow-release carbon source matrix filler layer and a surface gravel filler layer.

[0034] As a preferred solution, the downstream flow pool and the upstream flow pool are separated by an intermediate wall, and the bottoms of the downstream flow pool and the upstream flow pool are connected, sewage flows from the surface of the downstream flow pool to the bottom of the downstream flow pool and flows into the bottom of the upstream flow pool through the bottom connection, and then flows out through the surface of the upstream flow pool, wherein the surface of the upstream flow pool has an aerated aerobic zone, and the surface of the downstream flow pool has a reflow aerobic zone, part of the sewage in the aerobic zone of the upstream flow pool is reflowed to the reflow aerobic zone on the surface of the downstream flow pool through a reflow pump, and the bottoms of the upstream flow pool and the downstream flow pool are both anaerobic zones.

[0035] The present invention utilizes the water flow characteristics of the composite vertical flow artificial wetland (downflow pool, upstream pool), adds a glass porous cross-linked modified slow-release carbon source matrix to the bottom filler layer, and forms an anoxic denitrification environment at the bottom of the pool body; utilizes the surface aeration system of the upstream pool to form an aerobic environment on the surface of the upstream pool, and produces a large number of electron donors in the aerobic environment; at the same time, returns part of the sewage from the upstream pool to the downstream pool, and returns the electron donors to the aerobic zone through the surface of the downstream pool and then flows to the anaerobic area at the bottom of the pool to promote denitrification. Based on artificial wetlands, this method combines the A / O process principle to form anoxic zones and aerobic zones in artificial wetlands, and returns part of the sewage in the aerobic zone to the front end, further improving the nitrogen and phosphorus removal effects of the system. The relevant design layout of the composite vertical flow artificial wetland is shown in the present invention. Figure 1 and Figure 2 .

[0036] Because the composite vertical flow artificial wetland is divided into a downstream pool and an upstream pool, the sewage passes through the packing layer twice under the same floor space conditions, which greatly improves the removal efficiency of pollutants. At the same time, adding nano zero-valent iron to the artificial wetland packing layer, nano zero-valent iron as a deoxidizer, can make the lower layer of the artificial wetland in an anaerobic / anoxic environment, and the composite vertical flow artificial wetland can increase the residence time of sewage in the lower layer, ensure the denitrification reaction of denitrifying bacteria, and the polyphosphate bacteria release phosphorus anaerobically and consume part of the ammonia nitrogen, thereby improving the denitrification efficiency. A solar surface aeration device is set on the surface of the upstream pool to make the surface of the upstream pool in an aerobic environment, so that the polyphosphate bacteria excessively absorb phosphorus, organic matter is degraded by microorganisms, and the nitrification reaction of nitrifying bacteria is beneficial to the denitrification and phosphorus removal efficiency of the system. At the same time, part of the mixed liquid in the upstream pool is pumped back to the downstream pool to further degrade the nitrification reaction products.

[0037] Compared with the prior art, the present invention has the following beneficial effects: (1) The glass porous cross-linked modified slow-release carbon source matrix filler layer is used to greatly improve the nitrogen and phosphorus removal effect of the constructed wetland, and it can operate at low temperatures and has strong stability; (2) Effectively utilize the water flow characteristics of the composite vertical flow artificial wetland (downflow pool, upflow pool), combined with the A / O process principle, greatly improve the nitrogen and phosphorus removal effect of the artificial wetland system, and effectively solve the problem of urban sewage treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0039] Figure 1 Schematic diagram of the composite vertical flow constructed wetland.

[0040] Figure 2 Schematic diagram of the process flow of composite vertical flow constructed wetland.

[0041] Figure 3 Schematic diagram of the experimental device in Example 1 of the present invention. DETAILED DESCRIPTION

[0042] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0043] Example 1 The preparation of the glass porous cross-linked modified slow-release carbon source matrix in the present invention is as follows: 1. Preparation of porous glass matrix (1) Mix 30 parts of glass waste (particle size -150 mesh), 1 part of borax powder (particle size -150 mesh), 1 part of sodium phosphate powder (particle size -150 mesh), 15 parts of kaolin (particle size -150 mesh), 20 parts of blast furnace dust (particle size -150 mesh), 1 part of calcium carbonate foaming agent (particle size -600 mesh), and 1 part of magnesium carbonate foaming agent (particle size -600 mesh).

[0044] (2) Load the powder batch into a mold and place it in a reactor; (3) Heating to 40°C at a heating rate of 15°C / min, preheating time 15 min; (4) Heating to 800°C at a heating rate of 15°C / min, melting time 40 min; (5) Heating to 1000°C at a heating rate of 15°C / min and sintering time of 30 min; (6) The temperature was lowered to 500°C at a cooling rate of 20°C / min, and finally naturally cooled to room temperature to obtain a glass porous matrix loaded with nano-zero-valent iron.

[0045] 2. Preparation of modified slow-release carbon materials (1) crushing rice straw node cellulose to 0.5-1 cm to obtain rice straw node cellulose particles; (2) Soaking the rice straw cellulose particles in a 2% mass concentration sodium hydroxide solution, heating them in a water bath at 90°C, and keeping the water bath at a constant temperature for 4 hours for modification preparation; (3) After washing, the mixture was placed in a drying oven at 105°C and dried until the powder particle size reached -150 mesh, thereby obtaining a modified slow-release carbon material.

[0046] 3. Preparation of glass porous cross-linked modified slow-release carbon source matrix (1) 30 parts of the modified slow-release carbon material obtained above and 100 parts of water were added to a reaction kettle, heated to 65°C, stirred at a constant temperature, and gelatinized for 2 hours to obtain a gelatinized liquid; (2) The reactor was heated to 140°C, and 3 parts of polyvinyl alcohol (PVA), 40 parts of the above-mentioned gelatinized liquid, 40 parts of a glass porous matrix, and 1 part of a sodium bicarbonate foaming agent were added and stirred at a constant temperature for 1 hour; (3) Take out the mixture and inject it into the mold. After it reaches room temperature, transfer it to a low-temperature box and freeze it at -12℃ for 1 hour to freeze it into shape.

[0047] The present invention simulates a composite vertical artificial wetland, specifically as follows: The test sewage was tail water from a sewage treatment plant in Liuyang. After measurement, COD Cr The content is 27.33mg / L, BOD5 content is 5.82mg / L, NH3-N content is 1.45mg / L, TN content is 9.46mg / L, SS content is 8.22mg / L, and TP content is 0.255mg / L.

[0048] The simulated artificial wetland test device is made of plexiglass and consists of two cubic containers, simulating the downstream flow pool and the upstream flow pool respectively. The dimensions of both containers are 1m×1m×1m. The water level is controlled at 0.9m high and the surface hydraulic load is 0.9 m 3 / (m 2 ·d), the hydraulic retention time of sewage in the device is 24 h. This combined equipment and the downstream flow tank adopt a downward water distribution method. The sewage flows from top to bottom, connected by a pipe with a diameter of φ50 mm at the bottom, flows to the bottom of the upstream flow tank, and flows from bottom to top, and is discharged at the outlet of the upstream flow tank. At the same time, a pipe with a diameter of φ50 mm and a return pump are set to return part of the sewage from the upstream flow tank to the downstream flow tank.

[0049] A water inlet perforated pipe with a diameter of φ50 mm and an opening of φ7.5 mm is arranged on the upper layer of the downstream pool of the simulated composite vertical flow artificial wetland test device. The surrounding area is covered with gravel (particle size 10-30 mm) with a thickness of 100-150 mm. The bottoms of the two containers are connected by a φ50 mm pipe. The outlet of the upstream pool is located at a height of 0.9 m.

[0050] The filling layers from bottom to top are 20cm thick 10-30mm crushed stone filling layer, 40cm thick glass porous cross-linked modified slow-release carbon source matrix layer, 10cm thick 5-10mm crushed stone filling layer, and 10cm thick 10-30mm crushed stone filling layer.

[0051] The wetland plants are selected to be planted alternately with canna and yellow iris, with a planting density of 25 plants / m 2 .

[0052] The temperature was maintained at 30℃, and the sewage entered the device through the water distribution pipes. The experiment was started after the treatment effect of the reactor was stable. After the hydraulic retention time was 24h, the water outlet of the outlet pipe was monitored. After measurement, the removal rates of various pollutants in the outlet water of the device were shown in Table 1.

[0053]

[0054] According to the above results, except for total nitrogen, the effluent concentrations of various pollutant indicators all meet the Class IV standard for surface water, and the effluent concentration of total nitrogen is more than 50% lower than the first-level standard of "Hunan Province Urban Wastewater Treatment Plant Major Water Pollutant Discharge Standard" (DB43 / T1546-2018), greatly reducing the pollution load of various pollutants entering rivers and lakes.

Claims

1. A composite vertical flow artificial wetland, characterized by: It comprises a glass porous cross-linked modified slow-release carbon source matrix filler layer, wherein the glass porous cross-linked modified slow-release carbon source matrix is ​​prepared by cross-linking reaction between a glass porous matrix loaded with nano zero-valent iron and an alkali-treated modified biocarbon material.

2. A composite vertical flow artificial wetland according to claim 1, characterized in that: The preparation process of the glass porous cross-linked modified slow-release carbon source matrix is ​​as follows: the alkali-treated modified biocarbon material and water are mixed and heated to gelatinize to obtain a gelatinized liquid; the gelatinized liquid is mixed with polyvinyl alcohol, a foaming agent and a glass porous matrix loaded with nano zero-valent iron to undergo a cross-linking reaction, and then freeze-formed to obtain the obtained product.

3. A composite vertical flow artificial wetland according to claim 2, characterized in that: The mass ratio of the gelatinized liquid, polyvinyl alcohol, the glass porous matrix loaded with nano-zero-valent iron and the foaming agent is (40-50):(3-5):(40-50):(1-2).

4. A composite vertical flow artificial wetland according to claim 2 or 3, characterized in that: The heating gelatinization conditions are: temperature of 40-70°C and time of 1-3h; The conditions of the cross-linking reaction are: temperature of 100-140°C and time of 1-1.5h; The freezing molding conditions are: temperature of -15 to -12°C and time of 1 to 1.5 hours.

5. The composite vertical flow artificial wetland according to claim 1, characterized in that: The preparation process of the glass porous matrix loaded with nanometer zero-valent iron is as follows: glass waste, borax powder, sodium phosphate powder, kaolin, blast furnace dust and foaming agent are mixed and calcined to obtain the matrix.

6. The composite vertical flow artificial wetland according to claim 5, characterized in that: The mass parts of the glass waste are 30 to 40 parts; The mass portion of the borax powder is 1 to 2 parts; The mass portion of the sodium phosphate powder is 1 to 2 parts; The mass parts of the kaolin are 15 to 20 parts; The mass fraction of the blast furnace dust is 20-30 parts; The mass fraction of the foaming agent is 1 to 2 parts.

7. The composite vertical flow artificial wetland according to claim 5, characterized in that: The calcination process is: firstly heat to 400-450°C for preheating for 10-20 minutes, then continue to heat to 800-900°C for melting for 30-40 minutes, then continue to heat to 1000-1100°C for sintering for 20-40 minutes, then cool to 500-800°C, and then naturally cool to room temperature.

8. The composite vertical flow artificial wetland according to claim 1, characterized in that: The alkali-treated modified biochar material is prepared by soaking the biochar material in a sodium hydroxide solution.

9. The composite vertical flow artificial wetland according to claim 1, characterized in that: The composite vertical flow artificial wetland is divided into a downflow pool and an upflow pool. The fillers in the downflow pool and the upflow pool include a bottom crushed stone filler layer, a glass porous cross-linked modified slow-release carbon source matrix filler layer and a surface crushed stone filler layer.

10. The composite vertical flow artificial wetland according to claim 9, characterized in that: The downstream flow pool and the upstream flow pool are separated by an intermediate wall, and the bottoms of the downstream flow pool and the upstream flow pool are connected. Sewage flows from the surface of the downstream flow pool to the bottom of the downstream flow pool and flows into the bottom of the upstream flow pool through the bottom connecting portion, and then flows out through the surface of the upstream flow pool. The surface of the upstream flow pool has an aerated aerobic zone, and the surface of the downstream flow pool has a reflow aerobic zone. Part of the sewage in the aerobic zone of the upstream flow pool is reflowed to the reflow aerobic zone on the surface of the downstream flow pool through a reflow pump, and the bottoms of the upstream flow pool and the downstream flow pool are both anaerobic zones.

Images