Method for enhancing treatment of tail water with low carbon nitrogen ratio by using constructed wetland-microbial fuel cell

Abstract

The invention relates to a method for treating sewage, in particular to a method for treating low-carbon-nitrogen-ratio tail water by an enhanced constructed wetland-microbial fuel cell. The method comprises the following steps: pretreating agricultural solid waste raw materials, preparing fermentation liquor, constructing a constructed wetland-microbial fuel cell system taking pyrite as a main filler, preparing the agricultural solid waste fermentation liquor to strengthen the constructed wetland-microbial fuel cell to treat low-carbon-nitrogen-ratio tail water, and utilizing the agricultural solid wastes. The constructed wetland-microbial fuel cell is decomposed into a low-molecular carbon source which is more easily utilized by heterotrophic microorganisms through anaerobic fermentation, the biodegradability of sewage is improved, and the growth and reproduction of denitrifying bacteria in the wetland are promoted, so that the nitrogen removal effect of the constructed wetland-microbial fuel cell on tail water of an urban sewage treatment plant is improved; and the method has good environmental benefits, social benefits and economic benefits.

Description

Technical Field

[0001] The invention belongs to a sewage treatment method, and specifically relates to a method for strengthening artificial wetland-microbial fuel cell to treat low carbon-nitrogen ratio tail water. Background Art

[0002] With the rapid development of urbanization, the surge in population and the continuous improvement of social and economic levels, the composition and proportion of pollutants in domestic sewage have also changed, and the total nitrogen content has increased significantly, resulting in the tailwater of urban sewage treatment plants showing the characteristics of low carbon and high nitrogen. Excessive nitrogen in the tailwater will cause eutrophication of the receiving water body, seriously threatening the balance of the ecosystem and the health of the people. Therefore, the research on low carbon-nitrogen ratio tailwater treatment technology has become the key to the sustainable utilization and development of water resources.

[0003] The constructed wetlands-microbial fuel cell system (CWs-MFC) combines the advantages of low construction and operation costs of the constructed wetland system and small capacity of the microbial fuel cell system, taking into account the dual functions of sewage treatment and biopower generation, thereby achieving environmental and economic benefits simultaneously. It is a new ecological treatment technology with broad application prospects. However, the influent carbon source is the energy source of heterotrophic microorganisms in the constructed wetland-microbial fuel cell system and the electron donor in the denitrification process. It is an important factor affecting the denitrification process and denitrification capacity. The low carbon and high nitrogen characteristics of the tail water of the sewage treatment plant often lead to insufficient carbon source in the denitrification process of the system, resulting in poor denitrification effect of the final tail water. At the same time, the low carbon-nitrogen ratio of the tail water will also affect the reproduction of heterotrophic electrogenic bacteria in the system, thereby affecting the power generation effect of the system. The above problems can usually be alleviated by adding an external carbon source. At present, commonly used external carbon sources include pure carbon sources (such as glucose, sodium acetate, methanol, etc.), synthetic biodegradable polymer carbon sources (such as polyhydroxyalkanoates, polylactic acid, polycaprolactate, etc.) and slow-release agricultural solid waste carbon sources (including corn cobs, straw, peanut shells, etc.). Among them, pure carbon sources and synthetic polymer carbon sources have high costs and single nutrients, and their promotion and application are greatly limited. In comparison, agricultural solid waste carbon sources contain a large amount of cellulose, high organic matter content, wide sources, and low prices. They are a very potential external carbon source and are in line with the environmental protection concept of "waste treatment". However, the release process of agricultural solid waste carbon sources based on plant cellulose is complex, the release amount is unstable, and there are a large number of residues in the artificial wetland-microbial fuel cell system, which leads to blockage of the wetland matrix and affects the service life of the wetland; in addition, the utilization rate of agricultural solid waste carbon sources is low, and only a small amount actually participates in the microbial denitrification process, resulting in an increase in the concentration of organic matter in the effluent of the artificial wetland-microbial fuel cell system, and there is a risk of secondary pollution. Summary of the invention

[0004] The purpose of the present invention is to provide a method for strengthening artificial wetland-microbial fuel cell treatment of low carbon nitrogen ratio tail water, which collects agricultural solid waste (including corn cobs, straw, peanut shells, etc.) and then performs anaerobic fermentation to prepare fermentation liquid, so that the plant cellulose in the agricultural solid waste is decomposed into low molecular carbon sources, such as acetic acid, propionic acid, humic acid, etc. These decomposition products are more easily absorbed and utilized by denitrifying bacteria and electrogenic bacteria, thereby improving the denitrification effect and power generation performance of the artificial wetland-microbial fuel cell system. The present invention can not only improve the denitrification effect and power generation performance of the system for deep denitrification of tail water from sewage treatment plants, but also recycle agricultural solid waste, and has important promotion value for agricultural energy conservation and environmental protection solid waste resource utilization.

[0005] The objective of the present invention is achieved through the following technical solutions: A method for strengthening artificial wetland-microbial fuel cell to treat low carbon-nitrogen ratio tail water, the treatment method comprising the following steps: (1) Pretreatment of agricultural solid waste raw materials: Agricultural solid waste, including corn cobs, straw, and peanut shells, is dried and cut into small pieces of 1 to 2 cubic centimeters or small pieces of 1 to 2 centimeters long as raw materials for fermentation liquid; after washing with distilled water for 3 times, it is placed in an oven at 80°C and dried to constant weight, and then placed in a sealed bag and placed in a desiccator for storage; (2) Preparation of fermentation liquid: Add completely dry agricultural solid waste, including corn cobs, straw, peanut shells, anaerobic activated sludge or EM anaerobic fermentation compound bacteria, and tap water to the fermentation tank; then add trace element liquid to the fermentation tank; after the fermentation tank is sealed and stirred, after anaerobic fermentation in the fermentation tank for 5 to 40 days, inject the fermentation liquid into the water storage tank through the outlet and fully mix it with the tail water of the sewage treatment plant; The construction of an artificial wetland-microbial fuel cell system with pyrite as the main filler includes the following steps: 1) Construct an artificial wetland system: A vertical upflow wetland system is used. Pebbles 5 to 10 cm high are laid at the bottom of the system as a supporting layer. Pyrite with a particle size of 2 to 5 cm and sand, gravel, expanded clay, zeolite, volcanic rock, coal slag, blast furnace slag with a particle size of 1 to 3 cm are mixed in the upper main filling layer. At least one or more matrices are selected. The height of the main filling layer is 50 to 150 cm, and the porosity is 30 to 50%.

[0006] 2) Pretreatment of carbon fiber felt electrode: Soak the carbon fiber felt in acetone for 3 hours to remove the oil-soluble substances on the electrode surface, and then rinse with deionized water until the pH is neutral; boil the carbon fiber felt in deionized water, change the water every 30 minutes, and boil it for 6 times in a row, then take out the carbon fiber felt and place it in an oven at 80°C for 2 hours; use two titanium wire meshes to sandwich the pretreated carbon fiber felt and fix it with titanium wire to assist the carbon fiber electrode in collecting electrons; 3) Constructing an artificial wetland-microbial fuel cell system: placing two titanium wire mesh-carbon fiber felts at the air-water interface on the surface of the artificial wetland system and embedded in the anaerobic zone inside the artificial wetland system as the cathode and anode respectively; the distance between the anode and cathode carbon fiber felts is 15 to 30 cm, connected by an insulated copper wire, and connected to an external resistor of 500 to 1500 ohms to form a closed circuit; a voltmeter is connected in parallel with the external resistor to record the voltage generated by the artificial wetland-microbial fuel cell in real time; select one or more of the emergent plants calamus, reed, water celery, canna, etc. or the floating plants water hyacinth, water lily, duckweed, and plant them on the surface of the mixed filler matrix at a planting density of 10 to 30 plants / square meter; (4) Adding agricultural solid waste fermentation liquid to strengthen the artificial wetland-microbial fuel cell to treat low carbon-nitrogen ratio tail water, the steps are as follows: The anaerobic fermentation tank, the water storage tank and the artificial wetland-microbial fuel cell are connected in series in sequence with a polyvinyl chloride water supply pipe; the fermentation liquid in the anaerobic fermentation tank after fermentation for 5 to 40 days is injected into the water storage tank, and after being fully mixed with the tail water of the urban sewage treatment plant, the ratio of chemical oxygen demand (COD) to total nitrogen (TN) of the sewage reaches 5 to 7, and then it is continuously injected into the artificial wetland-microbial fuel cell system from the bottom water inlet through a peristaltic pump. The sewage flows from bottom to top through the pebble supporting layer, the main filler anaerobic zone, the anode zone, and the cathode zone. The treated sewage is finally discharged from the overflow weir at the top of the system.

[0007] The method for strengthening artificial wetland-microbial fuel cell to treat low carbon-nitrogen ratio tail water is described, wherein the bottom of the artificial wetland is provided with a water inlet pipe, and the upper part is provided with an overflow weir.

[0008] The method for strengthening artificial wetland-microbial fuel cell to treat low carbon-nitrogen ratio tail water, the hydraulic retention time of the sewage in the artificial wetland-microbial fuel cell system is 3 to 5 days.

[0009] The method for treating low carbon-nitrogen ratio tail water by strengthening artificial wetland-microbial fuel cell, at the end of each hydraulic retention cycle, the concentrations of ammonia nitrogen, total nitrogen, total phosphorus and COD in the effluent of the system are measured and their corresponding removal rates are calculated. The method for enhancing the treatment of low carbon-nitrogen ratio tail water by artificial wetland-microbial fuel cell, the output voltage of the artificial wetland-microbial fuel cell should be measured regularly, and the corresponding electrochemical performance indicators, including current and current density, power and power density and coulombic efficiency, are calculated to evaluate the effect of artificial wetland-microbial fuel cell on tail water treatment and power generation performance.

[0010] The present invention has the following excellent effects: 1. Agricultural solid waste is widely available and inexpensive. It can be decomposed into low-molecular carbon sources that are more easily utilized by heterotrophic microorganisms through anaerobic fermentation, which improves the biodegradability of sewage and promotes the growth and reproduction of denitrifying bacteria in wetlands, thereby improving the nitrogen removal effect of artificial wetland-microbial fuel cells on the tail water of urban sewage treatment plants, and has good environmental benefits.

[0011] 2. The present invention adds agricultural solid waste fermentation liquid carbon source to the artificial wetland-microbial fuel cell system, which is beneficial for the anode to produce more abundant electrons, improve the power generation performance of the system, and at the same time realize the resource utilization of agricultural solid waste, with good economic benefits.

[0012] 3. The present invention adopts the method of mixing fermentation liquid with sewage to add the additional carbon source, thereby avoiding the residue blockage caused by directly adding agricultural solid waste into the artificial wetland. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a schematic diagram of the structure of the anaerobic fermentation tank and artificial wetland-microorganism natural battery system of the present invention.

[0014] Numbers in the figure: motor 1, feed inlet 2, rotating shaft 3, exhaust port 4, metal agitator 5, fermentation liquid discharge port 6, tail water fermentation liquid mixed sewage 7, peristaltic pump 8, water inlet 9, pebble supporting layer 10, anaerobic zone 11, anode zone 12, titanium mesh-carbon fiber felt anode 13, mixed filler matrix 14, cathode zone 15, titanium mesh-carbon fiber felt cathode 16, overflow weir 17, aquatic plants 18, external resistor 19, voltmeter 20, drain outlet 21. DETAILED DESCRIPTION

[0015] In order to further explain the technical means and effects adopted by the present invention, the technical solution of the present invention is further described below through specific implementation methods, but the present invention is not limited to the scope of the embodiments.

[0016] The anaerobic activated sludge used in the present invention is taken from an anaerobic digestion tank of a sewage treatment plant, and the sludge concentration is 4550-7230 mg / L.

[0017] The anaerobic fermentation composite bacteria used in the present invention are agricultural EM anaerobic composting bacteria, which mainly include photosynthetic bacteria, lactic acid bacteria, yeast, actinomycetes and the like.

[0018] In a first aspect, an embodiment of the present invention provides a method for preparing agricultural solid waste fermentation liquid, comprising the following steps: Pretreatment of agricultural solid waste raw materials: Dry agricultural solid waste (including corn cobs, straw, peanut shells, etc.) and cut them into small pieces of 1 to 2 cubic centimeters or small pieces of 1 to 2 centimeters long as raw materials for fermentation liquid. After washing with distilled water for 3 times, put them in an oven at 80°C to constant weight, and then put them into sealed bags and store them in a desiccator for later use.

[0019] Preparation of fermentation liquid: Add 200-500 g of completely dried agricultural solid waste (including corn cobs, straw, peanut shells, etc.), 0.2-3 liters of anaerobic activated sludge or 100-500 g of EM anaerobic fermentation compound bacteria, and 17-19 liters of tap water to a 20-liter fermentation tank. Then add 40 ml of trace element solution to the fermentation tank. Among them, each liter of trace element solution contains the following composition: 0.1-2 g of boric acid, 0.01-0.2 g of zinc sulfate heptahydrate, 0.1-1.5 g of manganese sulfate, 0.05-0.2 g of copper sulfate pentahydrate, 0.01-0.05 g of cobalt sulfate heptahydrate, 0.1-0.5 g of ammonium heptamolybdate tetrahydrate, and 0.01-0.5 g of potassium iodide. Use 10% HCl and NaOH to adjust the pH of the trace element solution to 6.5-7.5. Before fermentation begins, seal the fermentation tank with a rubber ring, maintain the temperature in the fermentation tank at 25-40°C, and set the stirring speed at 120-170 rpm. Install a filter at the discharge port of the fermentation tank to prevent the fermentation residue from flowing out with the liquid. After 5-40 days of anaerobic fermentation in the fermentation tank, inject the fermentation liquid into the water storage tank through the outlet and fully mix it with the tail water of the sewage treatment plant.

[0020] In a second aspect, an embodiment of the present invention provides a construction of an artificial wetland-microbial fuel cell system based on pyrite as a main filler, comprising the following steps: Constructing an artificial wetland system: A vertical upflow wetland system is used, and 5-10 cm high pebbles (with a particle size of 2-5 cm) are laid at the bottom of the system as a supporting layer. The unique crystal structure of pyrite and the reducibility of iron and sulfur can remove heavy metals, organic pollutants and some inorganic elements in sewage through adsorption, coprecipitation and reduction. At the same time, pyrite has good electrical conductivity, stable properties, and is cheap and easy to obtain. Based on this, the present invention selects to mix and fill at least one or several matrices of pyrite with a particle size of 2-5 cm and sand, gravel, ceramsite, zeolite, volcanic rock, coal slag, and blast furnace slag with a particle size of 1-3 cm in the upper main filling layer according to a certain mass ratio. The height of the main filling layer is 50-150 cm, and the porosity is 30-50%. A water inlet pipe is set at the bottom of the artificial wetland, and an overflow weir is set at the top.

[0021] (2) Pretreatment of carbon fiber felt electrode: Soak the carbon fiber felt in acetone for 3 hours to remove the oil-soluble substances on the electrode surface, and then rinse with deionized water until the pH is neutral. Boil the carbon fiber felt in deionized water, change the water every 30 minutes, and boil it for 6 times in a row. Then take out the carbon fiber felt and place it in an oven at 80℃ for 2 hours. Use two titanium wire meshes to sandwich the pretreated carbon fiber felt and fix it with titanium wire to assist the carbon fiber electrode in collecting electrons.

[0022] (3) Construct an artificial wetland-microbial fuel cell system: Two titanium mesh-carbon fiber felts are placed at the air-water interface on the surface of the artificial wetland system and embedded in the anaerobic zone inside the artificial wetland system as cathode and anode. The distance between the anode and cathode carbon fiber felts is 15 to 30 cm, connected by an insulated copper wire, and connected to an external resistor of 500 to 1500 ohms to form a closed circuit. A voltmeter is connected in parallel with the external resistor to record the voltage generated by the artificial wetland-microbial fuel cell in real time. Select one or more of the emergent plants such as calamus, reed, water celery, canna, etc. or the floating plants such as water hyacinth, water lily, duckweed, etc., and plant them on the surface of the mixed filler matrix at a planting density of 10 to 30 plants / square meter.

[0023] In a third aspect, an embodiment of the present invention provides a method for treating low carbon-nitrogen ratio tail water by adding agricultural solid waste fermentation liquid to strengthen artificial wetland-microbial fuel cell, comprising the following steps: The anaerobic fermentation tank, water storage tank and artificial wetland-microbial fuel cell are connected in series with polyvinyl chloride water supply pipes. The fermentation liquid after 5 to 40 days of fermentation in the anaerobic fermentation tank is injected into the water storage tank, and after being fully mixed with the tail water of the urban sewage treatment plant, the ratio of chemical oxygen demand (COD) and total nitrogen (TN) of the sewage reaches 5 to 7. Then, a certain flow rate is controlled by a peristaltic pump and continuously injected into the artificial wetland-microbial fuel cell system from the bottom water inlet. The sewage flows from bottom to top through the pebble support layer, the main filler anaerobic zone, the anode zone, and the cathode zone. The treated sewage is finally discharged from the overflow weir at the top of the system. The hydraulic retention time of sewage in the artificial wetland-microbial fuel cell system is 3 to 5 days. At the end of each hydraulic retention cycle, the concentrations of ammonia nitrogen, total nitrogen, total phosphorus, and COD in the system effluent are measured and their corresponding removal rates are calculated; the output voltage of the artificial wetland-microbial fuel cell is measured regularly, and the corresponding electrochemical performance indicators (including current and current density, power and power density, and coulombic efficiency, etc.) are calculated to evaluate the effect of the artificial wetland-microbial fuel cell on tail water treatment and power generation performance.

[0024] The following is an explanation with examples in conjunction with the accompanying drawings. Example

[0025] Figure 1 It is a schematic diagram of the structure of the anaerobic fermentation tank and artificial wetland-microorganism natural battery system of the present invention; the corresponding numbers in the figure are: motor 1, feed inlet 2, rotating shaft 3, exhaust port 4, metal stirrer 5, fermentation liquid discharge port 6, tail water fermentation liquid mixed sewage 7, peristaltic pump 8, water inlet 9, pebble supporting layer 10, anaerobic zone 11, anode zone 12, titanium wire mesh-carbon fiber felt anode 13, mixed filler matrix 14, cathode zone 15, titanium mesh-carbon fiber felt cathode 16, overflow weir 17, aquatic plant 18, external resistor 19, voltmeter 20, drain outlet 21.

[0026] Pretreatment of agricultural solid waste raw materials: After drying, cut the agricultural solid waste corn cobs into small pieces of 1 to 2 cubic centimeters as the raw materials for fermentation liquid. After washing with distilled water for 3 times, put them in an oven at 80°C to a constant weight, and then put them into a sealed bag and store them in a desiccator for later use.

[0027] Preparation of fermentation liquid: 320 g of completely dried corn cobs, 1.6 liters of anaerobic activated sludge (sludge concentration of 6380 mg / L), and 18 liters of tap water were added to a fermenter with a volume of 20 liters through the feed port 2. Then 40 ml of trace element solution was added to the fermenter. Among them, each liter of trace element solution contains the following composition: 1.5 g of boric acid, 0.06 g of zinc sulfate heptahydrate, 0.8 g of manganese sulfate, 0.1 g of copper sulfate pentahydrate, 0.01 g of cobalt sulfate heptahydrate, 0.2 g of ammonium heptamolybdate tetrahydrate, and 0.18 g of potassium iodide. The pH of the trace element solution was adjusted to 7.0 using 10% HCl and NaOH. Before starting fermentation, the fermenter was sealed with a rubber ring, the temperature in the fermenter was maintained at 30 °C, and the stirring speed of the motor 1 and the metal stirrer 5 was set to 150 rpm. A filter was installed at the discharge port 6 of the fermenter to prevent the fermentation residue from flowing out with the liquid. After 25 days of anaerobic fermentation in the fermentation tank, the fermentation liquid is injected into the water storage tank through the discharge port 6 to be fully mixed with the tail water of the sewage treatment plant.

[0028] Constructing an artificial wetland system: A vertical upflow system is used. The artificial wetland reactor is made of plexiglass, including a cylinder with an inner diameter of 30 cm and a height of 50 cm and a cone with a height of 15 cm at the bottom, with a total volume of 38.9 liters and an effective volume of 31.8 liters. The drain outlets 21 are located 10 cm, 25 cm, and 40 cm below the top of the reactor. Pebbles (with a particle size of 2 to 3 cm) with a height of 15 cm are laid in the cone at the bottom of the artificial wetland as a supporting layer 10. The main filling layer on the upper part of the supporting layer 10 is filled with gravel (particle size 1 to 2 cm), ceramsite (particle size 1 to 2 cm) and pyrite (particle size 2 to 3 cm) in a mass ratio of 1:1:1, and the height of the main filling layer is 45 cm. A water inlet 9 is provided at the bottom of the artificial wetland, and an overflow weir 17 is provided at the top.

[0029] Pretreatment of carbon fiber felt electrode: Cut the 7 mm thick carbon fiber felt into squares with a side length of 25 cm and soak it in acetone for 3 hours to remove the oil-soluble substances on the electrode surface, then rinse it with deionized water until the pH of the washing liquid is neutral. Boil the carbon fiber felt in deionized water, change the water every 30 minutes, and boil it for 6 times in a row. Then take out the carbon fiber felt and place it in an oven at 80°C for 2 hours. Use two titanium wire meshes to sandwich the pretreated carbon fiber felt and fix it with titanium wire to assist the carbon fiber electrode in collecting electrons.

[0030] Constructing an artificial wetland-microbial fuel cell system: Two titanium wire mesh-carbon fiber felts are placed at the gas-water interface on the surface of the artificial wetland reactor as cathodes 16 and embedded in the anaerobic zone 11 inside the artificial wetland system as anodes 13. The distance between the carbon fiber felt anode 13 and the carbon fiber felt cathode is 20 cm, connected by an insulated copper wire, and connected to a 1000 ohm external resistor 18 to form a closed circuit. A voltmeter 20 is connected in parallel with the external resistor to record the voltage generated by the artificial wetland-microbial fuel cell in real time. Select the emergent plant Acorus calamus and plant it on the surface of the mixed filler matrix at a planting density of 15 plants / square meter.

[0031] The anaerobic fermentation tank, water storage tank and artificial wetland-microbial fuel cell are connected in series in sequence with a polyvinyl chloride water supply pipe with an inner diameter of 20 cm. Among them, the water storage tank is a plexiglass container with a length of 120 cm, a width of 100 cm, and a height of 100 cm, with a total volume of 1200 liters and an effective volume of 1080 liters. The fermentation liquid after 25 days of fermentation in the anaerobic fermentation tank is injected into the water storage tank, and after being fully mixed with the tail water of the sewage treatment plant, the ratio of chemical oxygen demand (COD) to total nitrogen (TN) reaches 6. Then, the BT100-2J peristaltic pump 8 is used to control the water inlet flow rate of 0.25 liters / minute to continuously inject the tail water fermentation liquid mixed sewage 7 in the water storage tank from the bottom water inlet 9 into the artificial wetland-microbial fuel cell system. The sewage flows from bottom to top through the pebble support layer, the main filler anaerobic zone 11, the anode zone 12, and the cathode zone 15, and is finally discharged from the overflow weir 17 at the top of the system. The hydraulic retention time of sewage in the artificial wetland-microbial fuel cell system is 3 days.

[0032] The ammonia nitrogen concentration of the tail water of the urban sewage treatment plant treated in this embodiment is 17.57 mg / L, the average total nitrogen concentration is 19.51 mg / L, the total phosphorus concentration is 0.59 mg / L, the COD concentration is 52.78 mg / L, and the pH value is 7.1. The total nitrogen concentration of the fermentation liquid after 25 days of fermentation in the anaerobic fermentation tank of this embodiment is 10.36 mg / L, the total phosphorus mass concentration is 0.17 mg / L, and the COD concentration is 482.31 mg / L. The ratio of COD to total nitrogen after the fermentation liquid and tail water are fully mixed is set to 6. According to the formula (COD 尾水 +COD 发酵液 ) / (TN 尾水 +TN 发酵液 )=6, the tail water volume in the storage tank is calculated to be 936 liters, the fermentation liquid volume is 144 liters, and the total volume of tail water, fermentation liquid and mixed sewage is 1080 liters.

[0033] Under the above conditions, the artificial wetland-microbial fuel cell reactor was continuously operated for 20 hydraulic retention time cycles (60 days), and the average removal rate of ammonia nitrogen in the tail water of the sewage treatment plant was 96.47%, the average removal rate of total nitrogen was 95.74%, the average removal rate of total phosphorus was 74.58%, and the average removal rate of COD was 52.97%. The comparison of the tail water treatment effect and power generation performance of the conventional artificial wetland-microbial fuel cell without adding agricultural solid waste fermentation liquid is shown in Table 1 and Table 2. The results show that the fermentation liquid made from anaerobic fermentation of agricultural solid waste corn cobs significantly improves the denitrification effect and power generation performance of the artificial wetland-microbial fuel cell system, and the effluent meets the Class A standard value of the "Pollutant Discharge Standard for Urban Wastewater Treatment Plants" (GB18918-2002) and the Class IV water quality requirements of the "Surface Water Environmental Quality Standard" (GB3838-2002).

[0034] Table 1 Comparison of tailwater quality of two artificial wetland-microbial fuel cell treatments

[0035] Table 2 Comparison of the electricity generation performance of two artificial wetland-microbial fuel cells in treating tail water .

Claims

1. A method for strengthening artificial wetland-microbial fuel cell to treat low carbon-nitrogen ratio tail water, characterized in that: The processing method comprises the following steps: (1) Pretreatment of agricultural solid waste raw materials: Agricultural solid waste, including corn cobs, straw, and peanut shells, is dried and cut into small pieces of 1 to 2 cubic centimeters or small pieces of 1 to 2 centimeters long as raw materials for fermentation liquid; after washing with distilled water for 3 times, it is placed in an oven at 80°C and dried to constant weight, and then placed in a sealed bag and placed in a desiccator for storage; (2) Preparation of fermentation liquid: Add completely dry agricultural solid waste, including corn cobs, straw, peanut shells, anaerobic activated sludge or EM anaerobic fermentation compound bacteria, and tap water to the fermentation tank; then add trace element liquid to the fermentation tank; after the fermentation tank is sealed and stirred, after anaerobic fermentation in the fermentation tank for 5 to 40 days, inject the fermentation liquid into the water storage tank through the outlet and fully mix it with the tail water of the sewage treatment plant; The construction of an artificial wetland-microbial fuel cell system with pyrite as the main filler includes the following steps: 1) Constructing artificial wetland system: adopt vertical upflow wetland system, lay 5-10 cm high pebbles as supporting layer at the bottom of the system, select the upper main filling layer to mix pyrite with particle size of 2-5 cm and sand, gravel, ceramsite, zeolite, volcanic rock, coal slag, blast furnace slag with particle size of 1-3 cm, at least one or several matrixes, the main filling layer height is 50-150 cm, and the porosity is 30-50%; 2) Pretreatment of carbon fiber felt electrode: Soak the carbon fiber felt in acetone for 3 hours to remove the oil-soluble substances on the electrode surface, and then rinse with deionized water until the pH is neutral; boil the carbon fiber felt in deionized water, change the water every 30 minutes, and boil it for 6 times in a row, then take out the carbon fiber felt and place it in an oven at 80°C for 2 hours; use two titanium wire meshes to sandwich the pretreated carbon fiber felt and fix it with titanium wire to assist the carbon fiber electrode in collecting electrons; 3) Constructing an artificial wetland-microbial fuel cell system: placing two titanium wire mesh-carbon fiber felts at the air-water interface on the surface of the artificial wetland system and embedded in the anaerobic zone inside the artificial wetland system as the cathode and anode respectively; the distance between the anode and cathode carbon fiber felts is 15 to 30 cm, connected by an insulated copper wire, and connected to an external resistor of 500 to 1500 ohms to form a closed circuit; a voltmeter is connected in parallel with the external resistor to record the voltage generated by the artificial wetland-microbial fuel cell in real time; select one or more of the emergent plants calamus, reed, water celery, canna, etc. or the floating plants water hyacinth, water lily, duckweed, and plant them on the surface of the mixed filler matrix at a planting density of 10 to 30 plants / square meter; (4) Adding agricultural solid waste fermentation liquid to strengthen the artificial wetland-microbial fuel cell to treat low carbon-nitrogen ratio tail water, the steps are as follows: The anaerobic fermentation tank, the water storage tank and the artificial wetland-microbial fuel cell are connected in series in sequence with a polyvinyl chloride water supply pipe; the fermentation liquid in the anaerobic fermentation tank after fermentation for 5 to 40 days is injected into the water storage tank, and after being fully mixed with the tail water of the urban sewage treatment plant, the ratio of chemical oxygen demand (COD) to total nitrogen (TN) of the sewage reaches 5 to 7, and then it is continuously injected into the artificial wetland-microbial fuel cell system from the bottom water inlet through a peristaltic pump. The sewage flows from bottom to top through the pebble supporting layer, the main filler anaerobic zone, the anode zone, and the cathode zone. The treated sewage is finally discharged from the overflow weir at the top of the system.

2. The method for treating low carbon-nitrogen ratio tail water by enhancing artificial wetland-microbial fuel cell according to claim 1, characterized in that: The bottom of the artificial wetland is provided with a water inlet pipe, and the upper part is provided with an overflow weir.

3. The method for treating low carbon-nitrogen ratio tail water by enhanced artificial wetland-microbial fuel cell according to claim 1, characterized in that: The hydraulic retention time of the sewage in the artificial wetland-microbial fuel cell system is 3 to 5 days.

4. The method for treating low carbon-nitrogen ratio tail water by enhancing artificial wetland-microbial fuel cell according to claim 3, characterized in that: At the end of each hydraulic retention cycle, the concentrations of ammonia nitrogen, total nitrogen, total phosphorus and COD in the system effluent are measured and their corresponding removal rates are calculated.

5. The method for treating low carbon-nitrogen ratio tail water by enhancing artificial wetland-microbial fuel cell according to claim 1, characterized in that: The output voltage of the artificial wetland-microbial fuel cell should be measured regularly, and the corresponding electrochemical performance indicators, including current and current density, power and power density, and coulombic efficiency, should be calculated to evaluate the effect of the artificial wetland-microbial fuel cell on tail water treatment and the power generation performance.

Images