Composite vertical flow constructed wetland

Abstract

The application discloses a composite vertical-flow constructed wetland. The composite vertical-flow constructed wetland comprises a glass porous crosslinking modified slow-release carbon source substrate filler layer, and the glass porous crosslinking modified slow-release carbon source substrate is prepared through crosslinking reaction of a glass porous substrate loaded with nano zero-valent iron and modified biochar material treated by alkali. The constructed wetland disclosed by the application can efficiently remove nitrogen and phosphorus, can stably operate in a low-temperature environment, has a small land occupation area and low cost, and can effectively solve the problem of urban sewage.

Description

Technical Field

[0001] This invention relates to a composite vertical flow constructed wetland, belonging to the field of water treatment technology. Background Technology

[0002] Currently, secondary effluent or effluent from urban wastewater treatment plants in my country still contains large amounts of nitrogen and phosphorus. Constructed wetlands, as an advanced nitrogen and phosphorus removal technology, are widely used in the treatment of secondary effluent or effluent from wastewater treatment plants. However, due to the low organic matter content and low carbon-to-nitrogen ratio in secondary effluent or effluent, the nitrification and denitrification processes of microorganisms are affected, resulting in low nitrogen and phosphorus removal efficiency. Furthermore, the low temperatures in winter negatively impact the operation of constructed wetlands. Therefore, developing a stable and efficient constructed wetland system to address urban wastewater problems is of great significance. Summary of the Invention

[0003] To address the shortcomings of existing technologies, the present invention aims to provide a composite vertical flow constructed wetland. This constructed wetland can efficiently remove nitrogen and phosphorus, operate stably even in low-temperature environments, has a small footprint, and is inexpensive, effectively solving urban wastewater problems.

[0004] To achieve the above-mentioned technical objectives, the present invention provides a composite vertical flow constructed wetland, which includes a glass porous cross-linked modified slow-release carbon source matrix filler layer. The glass porous cross-linked modified slow-release carbon source matrix is ​​prepared by cross-linking 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 this invention can effectively control carbon source release and has excellent heat preservation effect. Specifically, the micro-electrolysis of nano-zero-valent iron can promote the release of aromatic proteins and fulvic acid substances in the carbon source, thus accelerating the carbon release process of the solid carbon source. It also acts as an inorganic electron donor and reducing agent, providing electrons for denitrifying bacteria to perform anaerobic respiration, reducing nitrate nitrogen to N2 or NO2. - It also acts as a deoxygenating agent, ensuring an anaerobic environment for biological denitrification in the packing layer and promoting the enrichment of denitrifying microorganisms in the packing layer. The alkali-treated modified biochar material has enhanced carbon release performance and increased carbon release rate, while maintaining low nitrogen and phosphorus release. This modified slow-release carbon source acts as an organic electron donor, providing carbon for denitrifying bacteria. The glass porous cross-linked modified slow-release carbon source matrix of this invention significantly improves the denitrification efficiency and stability of constructed wetland systems through the synergistic denitrification of the modified slow-release carbon source, nano-zero-valent iron, and glass porous materials.

[0006] As a preferred embodiment, the preparation process of the glass porous crosslinked modified slow-release carbon source matrix is ​​as follows: alkali-treated modified biochar material is mixed with water and heated to gelatinize, resulting in a gelatinized liquid; the gelatinized liquid is then crosslinked with polyvinyl alcohol, a foaming agent, and a glass porous matrix loaded with nano-zero valent iron, followed by freeze-forming to obtain the final product.

[0007] Polyvinyl alcohol (PVA) possesses abundant hydroxyl (-OH) functional groups, enabling it to form stable sustained-release complexes through hydrogen bonding with biochar materials. This invention allows for the regulation of the carbon source release rate by controlling the molecular weight and cross-linking degree of PVA, as well as the pore structure of the biochar material.

[0008] As a preferred embodiment, the molecular weight of the polyvinyl alcohol is 170,000 to 220,000.

[0009] As a preferred option, the mass ratio of alkali-treated modified biochar material to water is (1~3):10.

[0010] As a preferred embodiment, the mass ratio of the gelatinized liquid, polyvinyl alcohol, glass porous matrix loaded with nano-zero valent iron, and foaming agent is (40~50):(3~5):(40~50):(1~2).

[0011] As a preferred embodiment, the foaming agent is sodium bicarbonate.

[0012] As a preferred embodiment, the conditions for heating and gelatinization are: temperature of 40~70℃ and time of 1~3h.

[0013] As a preferred embodiment, the conditions for the crosslinking reaction are: temperature of 100~140℃ and time of 1~1.5h.

[0014] As a preferred embodiment, the cryogenic forming conditions are: a temperature of -15 to -12°C and a time of 1 to 1.5 hours.

[0015] As a preferred embodiment, 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 matrix.

[0016] As a preferred embodiment, the glass waste comprises 30-40 parts by weight, the borax powder comprises 1-2 parts by weight, the sodium phosphate powder comprises 1-2 parts by weight, the kaolin comprises 15-20 parts by weight, the blast furnace dust comprises 20-30 parts by weight, and the foaming agent comprises 1-2 parts by weight.

[0017] Among them, blast furnace dust mainly serves as an iron and carbon source, and can be roasted and reduced to generate nano-zero-valent iron loaded onto a glass porous matrix.

[0018] As a preferred embodiment, the foaming agent comprises magnesium carbonate and calcium carbonate.

[0019] As a preferred embodiment, the particle size of the glass waste is -150 mesh to +200 mesh.

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

[0021] As a preferred embodiment, the sodium phosphate powder has a particle size of -150 mesh to +200 mesh.

[0022] As a preferred embodiment, the kaolin has a particle size of -150 mesh to +200 mesh.

[0023] As a preferred embodiment, the particle size of the blast furnace dust is -150 mesh to +200 mesh.

[0024] As a preferred embodiment, the particle size of the foaming agent is -600 mesh to +800 mesh.

[0025] As a preferred embodiment, the calcination process is as follows: first, heat to 400~450℃ for preheating for 10~20 minutes, then continue to heat to 800~900℃ for melting for 30~40 minutes, then continue to heat to 1000~1100℃ for sintering for 20~40 minutes, then cool down to 500~800℃, and then naturally cool to room temperature.

[0026] As a preferred option, the heating rate for the preheating, melting, and sintering processes is 10~20℃ / min.

[0027] As a preferred option, the cooling rate during the cooling process is 20~30℃ / min.

[0028] As a preferred embodiment, the alkali-treated modified biochar material is prepared by immersing the biochar material in a sodium hydroxide solution.

[0029] Alkali treatment can reduce the degree and strength of cellulose cross-linking. The principle is to use OH- to break the chemical bonds between lignin, cellulose, and hemicellulose, and also to break the chemical bonds within lignin itself, decomposing most of the lignin. Alkali-treated biochar materials exhibit enhanced carbon release performance, increased carbon release rate, and lower nitrogen and phosphorus release.

[0030] As a preferred embodiment, the biochar material is rice straw.

[0031] As a preferred embodiment, the length of the rice straw is 0.5~1cm.

[0032] The mass concentration of the sodium hydroxide solution is 1.5-2%.

[0033] As a preferred embodiment, the soaking temperature is 90~100℃ and the soaking time is 3~5h.

[0034] As a preferred embodiment, the composite vertical flow constructed wetland is divided into a downflow pool and an upflow pool. The filler material in the downflow pool and the upflow pool includes a bottom gravel filler layer, a glass porous cross-linked modified slow-release carbon source matrix filler layer, and a surface gravel filler layer.

[0035] As a preferred embodiment, the downflow pool and the upflow pool are separated by an intermediate wall, and their bottoms are connected. Wastewater flows from the surface of the downflow pool to its bottom and then through the bottom connection into the bottom of the upflow pool, before flowing out through the surface of the upflow pool. The surface of the upflow pool has an aerobic aeration zone, and the surface of the downflow pool has a recirculation aerobic zone. Part of the wastewater in the aerobic zone of the upflow pool is recirculated back to the recirculation aerobic zone on the surface of the downflow pool by a recirculation pump. The bottoms of both the upflow pool and the downflow pool are anaerobic zones.

[0036] This invention utilizes the water flow characteristics of a composite vertical flow constructed wetland (downflow tank and upflow tank). A porous, cross-linked, modified slow-release carbon source matrix is ​​added to the bottom packing layer to create an anoxic denitrification environment at the bottom of the tank. A surface aeration system in the upflow tank creates an aerobic environment on its surface, generating a large number of electron donors. Simultaneously, a portion of the wastewater from the upflow tank is returned to the downflow tank, and the electron donors are returned via the surface of the downflow tank to the aerobic zone and then to the anaerobic zone at the bottom of the tank to promote denitrification. This method, based on the constructed wetland and incorporating the A / O process principle, creates anoxic and aerobic zones within the constructed wetland and returns a portion of the aerobic zone wastewater to the front end, further enhancing the system's nitrogen and phosphorus removal efficiency. The relevant design layout of the composite vertical flow constructed wetland is described in this invention. Figure 1 and Figure 2 .

[0037] Because the composite vertical flow constructed wetland consists of a downflow pool and an upflow pool, wastewater passes through the packing layer twice within the same floor space, significantly improving pollutant removal efficiency. Simultaneously, the addition of nano-zero-valent iron to the packing layer acts as a deoxygenating agent, creating an anaerobic / anoxic environment in the lower layer. This increases the wastewater's residence time in the lower layer, ensuring sufficient denitrification by denitrifying bacteria and anaerobic phosphorus release by polyphosphate-accumulating bacteria, which also consume some ammonia nitrogen, further enhancing nitrogen removal efficiency. Solar-powered surface aeration equipment on the surface of the upflow pool creates an aerobic environment, allowing polyphosphate-accumulating bacteria to excessively absorb phosphorus, organic matter to be degraded by microorganisms, and nitrification by nitrifying bacteria, all contributing to the system's nitrogen and phosphorus removal efficiency. Furthermore, a portion of the mixed liquor from the upflow pool is pumped back to the downflow pool for further degradation of nitrification products.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] (1) The glass porous cross-linked modified slow-release carbon source matrix filler layer is adopted, which greatly improves the nitrogen and phosphorus removal effect of the constructed wetland, and can operate at low temperature with strong stability.

[0040] (2) By effectively utilizing the water flow characteristics of the composite vertical flow constructed wetland (downward flow pool and upward flow pool) and combining the A / O process principle, the nitrogen and phosphorus removal effect of the constructed wetland system is greatly improved, effectively solving the problem of urban sewage treatment. Attached Figure Description

[0041] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0042] Figure 1 This is a schematic diagram of a composite vertical flow constructed wetland.

[0043] Figure 2 This is a schematic diagram of the process flow for a composite vertical flow constructed wetland.

[0044] Figure 3 This is a schematic diagram of the experimental apparatus in Embodiment 1 of the present invention. Detailed Implementation

[0045] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0046] Example 1

[0047] The glass porous crosslinked modified slow-release carbon source matrix of this invention is prepared as follows:

[0048] 1. Preparation of porous glass matrix

[0049] (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).

[0050] (2) Load the powder batch into the mold and place it into the reactor;

[0051] (3) Heat to 40℃ at a heating rate of 15℃ / min, with a preheating time of 15min;

[0052] (4) Heat to 800℃ at a heating rate of 15℃ / min, and melt for 40min;

[0053] (5) Heat to 1000℃ at a heating rate of 15℃ / min, and sinter for 30min;

[0054] (6) Cool down to 500℃ at a cooling rate of 20℃ / min, and finally cool naturally to room temperature to obtain a glass porous matrix loaded with nano-zero valent iron.

[0055] 2. Preparation of modified slow-release carbon materials

[0056] (1) After crushing the rice straw cellulose to 0.5-1cm, rice straw cellulose particles are obtained;

[0057] (2) Soak rice straw cellulose particles in a 2% sodium hydroxide solution and heat them in a water bath at 90°C for 4 hours to modify them.

[0058] (3) After washing, put it in a drying oven at 105°C and dry it until the particle size of the powder reaches -150 mesh, thus obtaining the modified slow-release carbon material.

[0059] 3. Preparation of glass porous cross-linked modified slow-release carbon source matrix

[0060] (1) Take 30 parts of the modified slow-release carbon material obtained above and 100 parts of water and add them to the reaction vessel. Heat to 65°C, stir at a constant temperature, and gelatinize for 2 hours to obtain a gelatinized liquid.

[0061] (2) Heat the reactor to 140°C, add 3 parts of polyvinyl alcohol (PVA), 40 parts of the above gelatinized liquid, 40 parts of glass porous matrix, and 1 part of sodium bicarbonate foaming agent, and stir at a constant temperature for 1 hour.

[0062] (3) Take out the mixture and inject it into the mold. After it reaches room temperature, transfer it to a low temperature box at -12℃ and freeze for 1 hour to form the shape.

[0063] This invention simulates a composite vertical constructed wetland, as detailed below:

[0064] The wastewater used in the test was effluent from a wastewater treatment plant in Liuyang. The COD was measured to be... Cr The content was 27.33 mg / L, BOD5 content was 5.82 mg / L, NH3-N content was 1.45 mg / L, TN content was 9.46 mg / L, SS content was 8.22 mg / L, and TP content was 0.255 mg / L.

[0065] The simulated artificial wetland experimental device is made of plexiglass and consists of two cubic containers, simulating a downflow pool and an upflow pool respectively. Each container measures 1m × 1m × 1m, with the water level controlled at a height of 0.9m and a surface hydraulic load of 0.9 m. 3 / (m 2 •d) The hydraulic retention time of wastewater in the device is 24 hours. This combined equipment and the downflow tank adopt a downflow water distribution method. Wastewater flows from top to bottom, connected by a φ50 mm pipe at the bottom, flowing to the bottom of the upflow tank. Wastewater then flows from bottom to top and exits at the outlet of the upflow tank. Simultaneously, a φ50 mm pipe and a return pump are installed to return a portion of the wastewater from the upflow tank to the downflow tank.

[0066] The simulated composite vertical flow constructed wetland test device has an inlet perforated pipe with a diameter of φ50mm and an opening of φ7.5mm installed in the upper layer of the downflow pool. The surrounding area is covered with gravel (particle size 10-30mm) with a thickness of 100-150mm. The bottoms of the two containers are connected by a φ50mm pipe. The outlet of the upflow pool is located at a height of 0.9m.

[0067] The filler layers, from bottom to top, consist of a 20cm thick 10-30mm crushed stone filler layer, a 40cm thick glass porous cross-linked modified slow-release carbon source matrix layer, a 10cm thick 5-10mm crushed stone filler layer, and a 10cm thick 10-30mm crushed stone filler layer.

[0068] Wetland plants should be planted alternately with canna lilies and yellow irises, at a planting density of 25 plants / m². 2 .

[0069] The temperature was maintained at 30℃. Wastewater entered the device through the distribution pipe. After the reactor treatment effect stabilized, the experiment was started. After a hydraulic retention time of 24 hours, the water effluent was monitored. The removal rates of various pollutants in the effluent were measured and are shown in Table 1.

[0070]

[0071] Based on the above results, except for total nitrogen, the effluent concentrations of all pollutants met the Class IV standard for surface water. The total nitrogen effluent concentration was more than 50% lower than the Class I standard of the "Hunan Provincial Standard for Discharge of Major Water Pollutants from Urban Wastewater Treatment Plants" (DB43 / T1546-2018), which greatly reduced the pollution load of various pollutants entering rivers and lakes.

Claims

1. A composite vertical flow constructed wetland, characterized in that: The material includes 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 a glass porous matrix loaded with nano-zero valent iron and an alkali-treated modified biocarbon material. The preparation process of the glass porous cross-linked modified slow-release carbon source matrix is ​​as follows: the modified biochar material treated with alkali is mixed with water and heated to gelatinize, so as 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 carry out a cross-linking reaction, and then frozen and molded to obtain the product. The mass ratio of the gelatinized liquid, polyvinyl alcohol, glass porous matrix loaded with nano-zero valent iron and foaming agent is (40~50):(3~5):(40~50):(1~2); 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 matrix. The mass fraction of the glass waste is 30-40 parts; The borax powder is 1 to 2 parts by weight; The sodium phosphate powder is in the form of 1 to 2 parts by weight; The mass fraction of the kaolin is 15-20 parts; The mass fraction of the blast furnace dust is 20-30 parts; The foaming agent is 1 to 2 parts by weight; The calcination process is as follows: first, heat to 400~450℃ for preheating for 10~20 minutes, then continue to heat to 800~900℃ for melting for 30~40 minutes, then continue to heat to 1000~1100℃ for sintering for 20~40 minutes, then cool down to 500~800℃, and then naturally cool to room temperature.

2. The composite vertical flow constructed wetland according to claim 1, characterized in that: The conditions for heating and gelatinization are: temperature 40~70℃, time 1~3h; The conditions for the crosslinking reaction are: temperature 100~140℃, time 1~1.5h; The conditions for cryogenic forming are: temperature of -15 to -12°C and time of 1 to 1.5 hours.

3. The composite vertical flow constructed wetland according to claim 1, characterized in that: The modified biochar material treated with alkali is prepared by immersing the biochar material in a sodium hydroxide solution.

4. The composite vertical flow constructed wetland according to claim 1, characterized in that: The composite vertical flow constructed wetland is divided into a downflow pool and an upflow pool. The filler material in the downflow pool and the upflow pool includes a bottom gravel filler layer, a glass porous cross-linked modified slow-release carbon source matrix filler layer, and a surface gravel filler layer.

5. A composite vertical flow constructed wetland according to claim 4, characterized in that: The downflow pool and the upflow pool are separated by an intermediate wall, and their bottoms are connected. Wastewater flows from the surface of the downflow pool to its bottom and then through the bottom connection into the bottom of the upflow pool, before flowing out through the surface of the upflow pool. The surface of the upflow pool has an aerobic aeration zone, and the surface of the downflow pool has a recirculation aerobic zone. Part of the wastewater in the aerobic zone of the upflow pool is recirculated back to the recirculation aerobic zone on the surface of the downflow pool by a recirculation pump. The bottoms of both the upflow pool and the downflow pool are anaerobic zones.

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