A modular microbial electricity generation coupled with photo / electrocatalysis energy-saving wastewater treatment system with adjustable water level and no aeration cathode required

Abstract

The present invention provides a modular microbial electricity-producing coupled photo / electrocatalytic energy-saving wastewater treatment system with an adjustable water level and an aeration-free cathode. The system inlet is industrial wastewater, which flows into the reactor from the bottom water inlet via a peristaltic pump, passes through the microbial anode chamber, a sand insulation layer, and an upper cathode chamber, and then flows out. Carbon rods are used as conductive media between the cathode and the anode. Filter cloths are used to isolate the various parts. When the wastewater flows out of the cathode area, it flows out in a tidal manner. When the cathode is located above the water layer, an air cathode is formed, which reduces the need for aeration, can meet the oxygen required for the cathode reaction, and save the electricity required for additional aeration. This reactor setting can not only reduce the footprint, but also utilize the ability of microorganisms to transform pollutants and generate electricity, coupled with the photoelectric response and catalytic ability of the cathode nanocatalyst, to improve the coupling system's ability to remove COD, TN, TOC, etc. in industrial wastewater.

Description

Technical Field

[0001] This invention belongs to the technical field of industrial wastewater treatment and energy utilization in water pollution control. It involves cathode water level changes and BiOI / g-C3N4 / Bi2WO6 and Co / g-C3N4 / Bi2WO6 nanocomposite catalysts, creating an energy-saving system for the synergistic treatment of industrial wastewater by coupling microbial electricity production with photoelectric / electrocatalysis. This system performs continuous multi-stage treatment of high-salinity and oily wastewater, efficiently removing water pollutants. This provides valuable insights into the development of low-carbon, high-efficiency wastewater treatment technologies. Background Art

[0002] Industrial wastewater contains high concentrations of organic pollutants, including recalcitrant organic matter. This type of wastewater is difficult to treat, highly toxic, and poorly biodegradable. Due to the diverse nature of industries within industrial parks and the unique nature of each industrial process, the resulting wastewater is complex in composition. Some industrial wastewater is highly saline, containing dissolved solids and organic matter, high salinity, and anions such as sodium and calcium cations and sulfate. Furthermore, oil extraction and processing generate hydrocarbon- and oil-containing wastewater, which poses significant risks to surface water, groundwater, and soil, and is challenging to treat. Currently, a variety of methods are being used to treat this type of wastewater, categorized by principle as physical, chemical, and biological. However, these technologies and their combinations have limitations. Some technologies suffer from high energy consumption, high operating costs, complex operation, and even secondary pollution.

[0003] Photoelectrocatalysis (PEC) involves dispersing a catalyst on a conductive support to serve as the anode or cathode. Applying an external voltage causes photogenerated electrons to transfer through a circuit to the cathode, where photogenerated holes accumulate on the catalyst surface, achieving electron-hole pair separation and improving photocatalytic efficiency. Microbial fuel cells (MFCs) utilize microbial growth to directly convert chemical energy in organic matter into electrical energy. Electrons are transferred from the anode to the cathode, generating an electric current, and oxygen reduction occurs in the aerobic zone of the cathode. Currently, combining photo / electrocatalysis with microbial electricity generation can improve the overall efficiency of the system for water treatment and pollutant degradation. It also provides a continuous source of electricity, eliminating the need for an external electric field for electrocatalysis. This reduces energy consumption and can increase operating costs. There are two types of cathodes in this process: air cathodes and submerged cathodes. The latter often require aeration to provide dissolved oxygen for the electrode-catalyzed oxygen reduction reaction, which affects the system's power generation and increases energy consumption due to aeration. Summary of the Invention

[0004] The purpose of the present invention is to couple the photoelectrocatalysis / electrocatalysis with the microbial fuel cell power generation system, and successfully build a modular, low-carbon, energy-saving, and efficient photoelectrocatalytic coupled microbial power generation system (PEC-MFC / EC-MFC) for treating industrial wastewater with a cathode that does not require aeration and has an adjustable water level. Oxygen is provided to the cathode in a tidal manner, and an air cathode is formed when the cathode is above the water layer, which reduces the need for aeration and has the characteristic of saving aeration energy consumption. By utilizing the ability of microorganisms to transform pollutants and generate electricity, coupled with the photoelectric response and catalytic ability of the cathode nanocatalyst, efficient treatment of industrial wastewater is achieved, the power generation capacity of the system is improved, treatment costs and aeration energy consumption are saved, and the problems of traditional processes for treating industrial wastewater requiring the use of large amounts of chemical reagents, high cost, high energy consumption, and low treatment efficiency are solved.

[0005] The technical solution of the present invention:

[0006] A modular microbial electricity generation coupled photo / electrocatalytic energy-saving wastewater treatment system with adjustable water level and no aeration cathode required, comprising:

[0007] The system comprises an anode chamber, an isolation layer, and a cathode chamber arranged from bottom to top; the anode chamber and the isolation layer are separated by filter cloth; the isolation layer and the cathode chamber are separated by non-conductive material (such as filter cloth, preferably cotton cloth); the anode draws electricity through a waterproof carbon rod and is connected to a waterproof carbon rod connected to the cathode; the wastewater operation mode is bottom-in and top-out; when a visible light source is applied above the cathode chamber, the system functions as a photoelectrocatalytic coupled microbial fuel cell; when no visible light is applied above the cathode chamber, the system functions as an electrocatalytic coupled microbial fuel cell.

[0008] The anode chamber is filled with activated carbon loaded with Shewanella electrogenic bacteria and is an anaerobic area;

[0009] The isolation layer is filled with sand of irregular shape;

[0010] The cathode chamber is filled with activated carbon loaded with catalytic material;

[0011] Two water outlet holes, one above and one below, which can be blocked with rubber plugs are left above the cathode chamber. One water outlet hole is located on the surface of the cathode chamber, and the other water outlet hole is located at a higher position. The upper water outlet hole is always open for overflow water and sampling. When the water level rises to the lower water outlet hole, an air cathode is formed on the cathode surface. When the lower water outlet hole is blocked, the water level rises to the upper water outlet hole. After sampling, the lower water outlet hole is opened to allow the water between the two water outlet holes to be discharged from the lower water outlet hole. After an air cathode is formed on the cathode surface again, the lower water outlet hole is blocked. When only the upper water outlet hole is used, the water level is high, causing the cathode to be immersed below the water level, and the cathode obtains dissolved oxygen diffused from the air through the surface liquid. The lower water outlet uses a tidal method to provide oxygen to the cathode, reducing the need for aeration and having the characteristic of saving aeration energy consumption. When the water level is at the lower water outlet hole, the voltage is 1.22 times that when the water level is at the upper water outlet hole, and the current is 1.35 times, thereby enhancing the power generation capacity of the system.

[0012] The cathode material of the system is loaded with nanocatalysts with photocatalytic properties. When the system is used as a photoelectrocatalytic coupled microbial fuel cell, the cathode catalytic material is loaded with BiOI / g-C3N4 / Bi2WO6 nanocomposite photocatalysts; when the system is used as an electrocatalytic coupled microbial fuel cell, the cathode catalytic material is loaded with Co / g-C3N4 / Bi2WO6 nanocomposite catalysts.

[0013] The BiOI / g-C3N4 / Bi2WO6 nanocomposite photocatalyst is prepared by calcination, hydrothermal and co-precipitation methods, and the Co / g-C3N4 / Bi2WO6 nanocomposite catalyst is prepared by calcination and hydrothermal methods;

[0014] The carbon rod connected to the cathode chamber and the carbon rod connected to the anode chamber are connected by an external resistor with a resistance of 10 to 10,000 Ω through an external wire;

[0015] The industrial wastewater treated by the photoelectrocatalytic coupled microbial fuel cell is saline wastewater, and the industrial wastewater treated by the electrocatalytic coupled microbial fuel cell system is oily wastewater;

[0016] The wastewater enters the high-level water pool with a flow meter controlling the flow rate, thus saving the electric energy of the pumping method.

[0017] The ratio of the anode chamber to the cathode chamber can be adjusted according to the actual wastewater treatment conditions.

[0018] Beneficial effects of the present invention: The present invention provides a modular energy-saving industrial wastewater treatment system with an adjustable water level and no need for aeration at the cathode stage, wherein a photoelectric / electrocatalytic cathode is coupled with a microbial electricity-generating anode to form a fuel cell system. The system realizes the coupling of photocatalysis or electrocatalysis with microorganisms. The coupled system can generate electricity while treating wastewater, and the treatment effect is relatively significant. The system uses a high-level water pool for water inlet to save pump-type electricity consumption. The system uses a tidal method to provide an aerobic environment for the cathode, and the air cathode form saves aeration energy consumption. The entire system occupies a small area, and the salt-containing wastewater and oil-containing wastewater are effectively treated by the PEC-MFC and EC-MFC systems respectively, which proves that the proposed new technology system and treatment system have high efficiency in treating wastewater. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a schematic diagram of the photoelectrocatalytic coupled microbial fuel cell system (PEC-MFC) device.

[0020] Figure 2 This is a schematic diagram of the electrocatalytic coupled microbial fuel cell system (EC-MFC) device.

[0021] Figure 3 Figure 2 shows the COD stability of the system's two-stage effluent. (a) shows the COD stability of the PEC-MFC two-stage effluent, using BiOI / g-C3N4 / Bi2WO6 as the cathode material; (b) shows the COD stability of the EC-MFC two-stage effluent, using Co / g-C3N4 / Bi2WO6 as the cathode material. The horizontal axis represents time (days), and the vertical axis represents COD concentration (mg / L).

[0022] Figure 4 This is the TN stability diagram of the two-stage effluent of PEC-MFC. BiOI / g-C3N4 / Bi2WO6 is used as the cathode loading material. The horizontal axis is time (day) and the vertical axis is TN concentration (mg / L).

[0023] Figure 5 This is the TOC stability diagram of the two-stage effluent of EC-MFC. Co / g-C3N4 / Bi2WO6 is used as the cathode loading material. The horizontal axis is time (day) and the vertical axis is TOC concentration (mg / L).

[0024] Figure 6 The UV spectra of the two-stage effluent from the system are shown in Figure 1. (a) shows the UV spectra of the two-stage effluent from the PEC-MFC, using BiOI / g-C3N4 / Bi2WO6 as the cathode material; (b) shows the UV spectra of the two-stage effluent from the EC-MFC, using Co / g-C3N4 / Bi2WO6 as the cathode material. The abscissa is absorbance (Abs), and the ordinate is wavelength (nm).

[0025] In the figure: 1 water pool; 2 water outlet pipe; 3 flow meter; 4 water inlet; 5 anode area; 6 filter cloth; 7 sand isolation layer area; 8 cathode area; 9 rubber plug; 10 water outlet A; 11 carbon rod; 12 wire; 13 external resistor; 14 container; 15 water outlet B. DETAILED DESCRIPTION

[0026] The following further illustrates the specific implementation of the present invention in combination with the technical solutions and drawings, which does not limit the scope of protection of the present invention.

[0027] like Figure 1 and Figure 2 As shown, the present invention provides a photoelectric / electrocatalytic coupled microbial fuel cell system for treating industrial wastewater. The coupled system has the following modular features, and its treatment design comprises:

[0028] The water pool 1 located in the high-level area is used for the wastewater to flow by gravity through the lower outlet pipe 2 into the bottom water inlet 4 of the photoelectric / electrocatalytic coupled microbial fuel cell reactor of the treatment system. A flow meter 3 is installed at the position of the water pipe 2 to control the flow rate of the wastewater gravity flow.

[0029] The wastewater flows from the bottom water inlet 4 into the anode area 5 filled with activated carbon loaded with Shewanella exoelectrogenic bacteria, and after being treated in the anode area 5, enters the sand isolation layer area 7 isolated by the filter cloth 6, and then flows into the cathode area 8 filled with activated carbon loaded with catalytic materials isolated by the filter cloth 6.

[0030] Two water outlets, A10 and B15, are located above the cathode region 8 and are plugged with rubber stoppers 9. Water outlet A10, located on the cathode surface, is used to tidal-supply oxygen to the cathode region 9, forming a surface air cathode on the cathode surface. When the water level submerges the cathode, water overflows through water outlet B15.

[0031] The anode region 5 and the cathode region 8 are led out using carbon rods 11 wrapped with waterproof tape to collect and conduct electrons. The carbon rods 11 are connected by wires 12 and connected to a 100Ω external resistor 13.

[0032] The water inlet 4, the anode area 5, the filter cloth 6, the sand isolation layer area 7, the cathode area 8, the rubber stopper 9, the water outlet A10, the carbon rod 11, the wire 12, the external resistor 13, and the water outlet B15 are all contained in a container 14 of a certain volume. The container 14 is a plastic shell and can be made of other materials.

[0033] Preparation of the anode: The Shewanella electrogenic bacteria are adsorbed on the granular activated carbon. The Shewanella electrogenic bacteria are a mixed bacteria cultured and domesticated from the bottom mud of the Yellow Sea waters in Dalian Xinghai Square. When the electrogenic potential of the bacteria is measured by a 232 reference electrode and is greater than 0.06V, it can be used.

[0034] Preparation of cathode: Mix a certain amount of nanocatalyst in deionized water in a beaker, weigh activated carbon in a certain proportion to the volume of the anode chamber and pour it into the beaker to mix. Let it stand for 24 hours to allow the catalytic material to be fully loaded on the activated carbon particles. Then place the beaker in a 60°C oven to dry and set aside.

[0035] Example 1

[0036] Combine Figure 1 First, the high-salt wastewater diluted 50 times is placed in the water pool 1, and flows into the water inlet 4 at the bottom of the photoelectrocatalytic coupled microbial fuel cell reactor through the water pipe 2. The flow rate of the wastewater is controlled by a flow meter 3 at a certain position of the water pipe 2, so that the wastewater stays in the reactor for 16 hours.

[0037] The wastewater flows from the bottom water inlet 4 into the anode area 5 filled with activated carbon loaded with Sheeva-type electrogenic bacteria. After being treated by microorganisms in the anode area 5, the wastewater flows into the sand isolation layer 7 and the cathode area 8 in sequence.

[0038] Wastewater flows out from the outlet hole A10 on the upper part of the cathode area 8. When the rubber stopper 9 plugs the outlet hole A10, the water level will exceed the cathode area 8. The part above the cathode area 8 can be used for sampling and testing, and then flows out through the outlet hole B15.

[0039] The cathode part is a photocathode. A visible light source is set 10 cm above the reactor to provide light energy. The photocathode is prepared as follows:

[0040] BiOI / g-C3N4 / Bi2WO6 catalyst was synthesized by calcination, hydrothermal and co-precipitation methods. For g-C3N4 synthesis, 60 g of urea was weighed and placed in a ceramic crucible, which was then placed in a muffle furnace and calcined to 550°C at a heating rate of 2°C / min, then maintained for 4 hours, and finally cooled to room temperature to obtain yellow solid g-C3N4, which was ground into powder.

[0041] Synthesis of g-C3N4 / Bi2WO6: First, 0.31g of g-C3N4 and 1.319g of sodium tungstate dihydrate were dispersed in 30mL of ethylene glycol and ultrasonically stirred for 30 minutes to form Solution A. Then, 1.94028g of bismuth nitrate pentahydrate was mixed in 30mL of ethylene glycol and ultrasonically stirred for 30 minutes to form Solution B. Solution B was then added to Solution A and ultrasonically stirred for 30 minutes. The mixture was then transferred to a 100mL polytetrafluoroethylene-lined autoclave, heated at 160°C for 12 hours, and naturally cooled to room temperature. Finally, the mixture was washed several times with alcohol and deionized water, collected by centrifugation, and dried at 60°C for 12 hours to obtain g-C3N4 / Bi2WO6, which was then ground into a powder.

[0042] Synthesis of BiOI: Dissolve 0.97 g of bismuth nitrate pentahydrate and 0.332 g of potassium iodide in 15 mL of ethylene glycol and stir for 30 minutes. The two solutions are then mixed for 15 minutes and transferred to a 100 mL polytetrafluoroethylene autoclave. The autoclave is heated at 160°C for 12 hours and allowed to cool to room temperature. The resulting solid BiOI is then washed several times with alcohol and deionized water, collected by centrifugation, and dried at 60°C for 12 hours to obtain a powder.

[0043] Synthesis of BiOI / g-C3N4 / Bi2WO6: 0.009 g BiOI and g-C3N4 / Bi2WO6 were dispersed in methanol under ultrasound assistance for 30 min, then washed and collected by centrifuge, dried at 60 °C for 12 h, and ground into powder.

[0044] BiOI / g-C3N4 / Bi2WO6 photocathode: Take 0.05g BiOI / g-C3N4 / Bi2WO6 and mix it evenly in 30ml deionized water. Weigh 20g activated carbon and pour it into the mixture. Let it stand for 24 hours, then place the beaker in a 60℃ oven to dry.

[0045] Example 2

[0046] Combine Figure 2 First, the oily wastewater is placed in the water pool 1 and flows into the water inlet 4 at the bottom of the electrocatalytic coupled microbial fuel cell reactor through the water pipe 2. The flow rate of the wastewater is controlled by a flow meter 3 at a certain position of the water pipe 2, so that the wastewater stays in the reactor for 16 hours.

[0047] The wastewater flows from the bottom water inlet 4 into the anode area 5 filled with activated carbon loaded with Sheeva-type electrogenic bacteria. After being treated by microorganisms in the anode area 5, the wastewater flows into the sand isolation layer 7 and the cathode area 8 in sequence.

[0048] Wastewater flows out from the outlet hole A10 on the upper part of the cathode area 8. When the rubber stopper 9 plugs the outlet hole A10, the water level will exceed the cathode area 8. The part above the cathode area 8 can be used for sampling and testing, and then flows out through the outlet hole B15.

[0049] Cathode preparation:

[0050] Co / g-C3N4 / Bi2WO6 catalyst was synthesized by calcination and hydrothermal method. For g-C3N4 synthesis, 60 g of urea was weighed and placed in a ceramic crucible, which was then placed in a muffle furnace and calcined to 550°C at a heating rate of 2°C / min, then maintained for 4 hours, and finally cooled to room temperature to obtain yellow solid g-C3N4, which was ground into powder.

[0051] Synthesis of Co / g-C3N4 / Bi2WO6: First, 0.31g g-C3N4 and 0.66g of sodium tungstate dihydrate were dispersed in 30ml of ethylene glycol and ultrasonically stirred for 30 minutes. This was referred to as Solution A. Subsequently, 1.94028g of bismuth nitrate pentahydrate and 0.0168g of cobalt nitrate were mixed and dissolved in 30ml of ethylene glycol and ultrasonically stirred for 30 minutes. This was referred to as Solution B. Solution B was then added to Solution A and ultrasonically stirred for 30 minutes. The mixture was then transferred to a 100ml polytetrafluoroethylene autoclave and heated at 160°C for 12 hours. The mixture was cooled naturally to room temperature and washed several times with alcohol and deionized water. The mixture was collected by centrifugation, dried at 60°C for 12 hours, and ground into a powder.

[0052] Co / g-C3N4 / Bi2WO6 cathode: Take 0.05g Co / g-C3N4 / Bi2WO6 and mix it in 30ml deionized water. Then weigh 20g activated carbon and pour it into the mixture. Let it stand for 24 hours, then place the beaker in a 60℃ oven to dry.

[0053] Example 3

[0054] Combine Figure 1 ,use Figure 1 The PEC-MFC device in the treatment of high-salt wastewater diluted 50 times, the reaction system residence time is 16 hours, sampling and testing are carried out to make a daily COD stability diagram, such as Figure 3 (a) in; combined Figure 2 ,use Figure 2 The EC-MFC device in the treatment of oily wastewater, the reaction system residence time is 16 hours, sampling and testing are carried out to make a daily COD stability diagram, such as Figure 3 (b) in the.

[0055] Example 4

[0056] Combine Figure 1 ,use Figure 1 The device in Figure 4Daily TN degradation stability curve for TN treatment of 50-fold diluted high-salt wastewater.

[0057] Example 5

[0058] Combine Figure 2 ,use Figure 2 The device in Figure 5 This is the TOC treatment status of oily wastewater and the daily TOC degradation stability chart.

[0059] Example 6

[0060] Combine Figure 1 ,use Figure 1 The PEC-MFC device in the reactor treats high-salinity wastewater diluted 50 times, and performs UV full spectrum scanning on the effluent of the two stages of the reactor to check the changes in organic matter in the effluent, such as Figure 6 (a) in; combined Figure 2 ,use Figure 2 The EC-MFC device in the reactor is used to treat oily wastewater. The effluent from the two stages of the reactor is scanned with UV spectrum to check the changes in organic matter in the effluent. Figure 6 (b) in the.

Claims

1. A modular microbial electricity generation coupled photo / electrocatalytic energy-saving wastewater treatment system with adjustable water level and no aeration cathode required, characterized by: include: The system comprises an anode chamber, an isolation layer, and a cathode chamber arranged from bottom to top; The anode chamber is separated from the isolation layer by filter cloth; The isolation layer and cathode chamber are separated by non-conductive material; the anode draws electricity through a waterproof carbon rod and connects to the waterproof carbon rod connected to the cathode; the wastewater flow mode is bottom-in and top-out; when a visible light source is applied above the cathode chamber, the system functions as a photoelectrocatalytic coupled microbial fuel cell; when no visible light is applied above the cathode chamber, the system functions as an electrocatalytic coupled microbial fuel cell; The anode chamber is filled with activated carbon loaded with Shewanella electrogenic bacteria and is an anaerobic area; The isolation layer is filled with sand in irregular shapes; The cathode chamber is filled with activated carbon loaded with catalytic material; Two water outlet holes are provided above the cathode chamber, which can be plugged with rubber plugs. One water outlet hole is located on the surface of the cathode chamber, and the other water outlet hole is located at a higher position. The cathode material of the system is loaded with a nanocatalyst having photocatalytic properties; when the system is used as a photoelectrocatalytic coupled microbial fuel cell, the cathode catalytic material is loaded with a BiOI / g-C3N4 / Bi2WO6 nanocomposite photocatalyst; when the system is used as an electrocatalytic coupled microbial fuel cell, the cathode catalytic material is loaded with a Co / g-C3N4 / Bi2WO6 nanocomposite catalyst; the BiOI / g-C3N4 / Bi2WO6 nanocomposite photocatalyst is prepared by calcination, hydrothermal and co-precipitation methods, and the Co / g-C3N4 / Bi2WO6 nanocomposite catalyst is prepared by calcination and hydrothermal methods; The industrial wastewater treated by the photoelectrocatalytic coupled microbial fuel cell is saline wastewater, and the industrial wastewater treated by the electrocatalytic coupled microbial fuel cell system is oily wastewater; The wastewater enters the high-level water pool with a flow meter controlling the flow rate, thus saving the electric energy of the pumping method.

2. The modular microbial electricity generation coupled photo / electrocatalytic energy-saving wastewater treatment system with adjustable water level and no aeration cathode according to claim 1 is characterized in that: The carbon rod connected to the cathode chamber and the carbon rod connected to the anode chamber are connected by an external resistor with a resistance value of 10 to 10,000 Ω via an external wire.

3. The modular microbial electricity generation coupled photo / electrocatalytic energy-saving wastewater treatment system with adjustable water level and no aeration cathode according to claim 1 is characterized in that: The ratio of the anode chamber to the cathode chamber can be adjusted according to the actual wastewater treatment conditions.

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