Method for strengthening microbial degradation of nitrogen-containing heterocyclic compound wastewater by photocatalytic oxygen supply

Abstract

The application discloses a method for strengthening microbial degradation of nitrogen-containing heterocyclic compound wastewater by photocatalytic oxygen supply. The method comprises the following steps: preparing a gas diffusion carbon cloth with a hydrophilic side and a strong hydrophobic side, placing the gas diffusion carbon cloth between a microbial reaction system and a photocatalytic water decomposition system, locating the hydrophilic side of the gas diffusion carbon cloth on the side of the microbial reaction system and locating the strong hydrophobic side on the side of the photocatalytic water decomposition system, and feeding the nitrogen-containing heterocyclic compound wastewater into the microbial reaction system and realizing photocatalytic oxygen supply and microbial degradation by light and dark alternation. The application constructs a photocatalytic oxygen evolution micro-aerobic / aerobic biological system, and oxygen generated by photocatalytic decomposition of water by a semiconductor material is transmitted to the microbial reaction system through the gas diffusion carbon cloth, so that the effect of strengthening micro-aerobic / aerobic biological degradation of the nitrogen-containing heterocyclic compound wastewater is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of treatment of nitrogen-containing heterocyclic compound wastewater, and relates to a method for enhancing microbial degradation of nitrogen-containing heterocyclic compound wastewater through photocatalytic oxygen supply. Background Art

[0002] Nitrogen-containing heterocyclic compounds are common pollutants in industrial wastewater. Because the ring structure of nitrogen-containing heterocyclic compounds is a closed conjugated system, nitrogen-containing heterocyclic compounds are usually structurally stable and difficult to degrade. They can exist in the environment for a long time and pose potential hazards to both the ecology and the human body.

[0003] Currently, the main methods for treating nitrogen-containing heterocyclic compound wastewater include physicochemical and biological methods. Physicochemical methods include photocatalytic degradation, ozone oxidation, membrane separation, and electrochemical oxidation. While effective and fast, they suffer from high costs, high energy consumption, and even secondary pollution. Common biological treatment technologies include aerobic and anaerobic biotechnology. Anaerobic biotechnology suffers from low degradation efficiency and poor stability, while aerobic biotechnology has high degradation efficiency and good effluent quality, making it widely used in wastewater treatment. However, for traditional aerobic biological treatment technology, the dissolved oxygen content in the water is crucial to the entire degradation system. To maintain sufficient dissolved oxygen in the biodegradation system, additional aeration devices are required to continuously replenish the dissolved oxygen in the aerobic biodegradation system, increasing operating costs and equipment energy consumption. It can also easily lead to the volatilization of pollutants, causing secondary air pollution. Physical, chemical, and biological methods have all been applied to treat refractory organic wastewater. In recent years, research on novel biological treatment technologies that enhance biological treatment effects through physicochemical means has attracted increasing attention.

[0004] At present, the sewage treatment method combining photocatalysis with microorganisms is mainly to photocatalyze the generation of oxidative active groups, thereby achieving the effect of oxidative destruction of most organic matter. Studies have shown that under light excitation, semiconductor materials produce photoexcited electron-hole pairs, which can produce superoxide radicals and hydroxyl radicals with oxygen and water. Different masking agents are used to explore the role of photoexcited holes, superoxide radicals and hydroxyl radicals in photoexcited hole-enhanced biological systems. A semiconductor-microorganism interface is developed to achieve efficient degradation and mineralization of difficult-to-degrade organic pollutants (pyridine, p-CP and AO7). It mainly accelerates biological reactions by using photogenerated holes and photogenerated electrons as electron acceptors / donors in the biodegradation process. Superoxide radicals and hydroxyl radicals are produced by photocatalytic semiconductor materials and water reactions to directly oxidize nitrogen-containing heterocyclic compounds (Shi Hefei, etal. BiVO4 / FeOOH semiconductor-microbe interface for enhanced visible-light-driven biodegradation of pyridine. Water Research, 2020, 187, 116464.). Using photocatalytic technology to pretreat organic wastewater can effectively improve its biodegradability, thereby ensuring smooth subsequent biodegradation and achieving the goal of removing organic matter and purifying the wastewater. However, this coupled technology suffers from issues such as large footprint, slow mass transfer rates, and cumbersome operation, resulting in a ceiling on the treatment efficiency of photocatalytic-biodegradable coupling.

[0005] Oxygen generated during water electrolysis has been widely used in many industrial applications, but the application of photocatalytic oxygen production for enhanced biodegradation of pollutants has not been reported. Summary of the Invention

[0006] In response to the problems of high mechanical aeration energy consumption, high gas loss, and gas volatilization pollution in existing aerobic biological treatment of nitrogen-containing heterocyclic compound wastewater, the present invention provides a method for enhancing microbial degradation of nitrogen-containing heterocyclic compound wastewater through photocatalytic oxygen supply. The method utilizes photocatalytic semiconductor materials to evolve oxygen, transfers oxygen through gas diffusion carbon cloth, realizes in-situ mass transfer of oxygen, and achieves microaerobic / aerobic biodegradation of nitrogen-containing heterocyclic compound wastewater.

[0007] The technical solution adopted in the present invention is as follows:

[0008] A method for enhancing microbial degradation of nitrogen-containing heterocyclic compound wastewater by photocatalytic oxygen supply is firstly prepared, and then a photocatalytic oxygen evolution microaerobic / aerobic biological system is constructed. The oxygen generated by the photocatalytic semiconductor material decomposing water is transferred to the microbial reaction system through the gas diffusion carbon cloth to carry out microaerobic / aerobic degradation of nitrogen-containing heterocyclic compound wastewater. The specific steps are as follows:

[0009] Step 1: Using a polytetrafluoroethylene (PTFE) dispersion, a semiconductor material having photocatalytic oxygen evolution capability is bonded to one side of a highly hydrophobic and porous carbon cloth;

[0010] Step 2: Spin coating the hydrophilic material on one side of another piece of highly hydrophobic and porous carbon cloth of the same size;

[0011] Step 3: Bonding the untreated sides of the two carbon cloths from Step 1 and Step 2 with a polytetrafluoroethylene dispersion, then heating to 200-400° C. and calcining to obtain a gas diffusion carbon cloth with one hydrophilic side and the other strongly hydrophobic side;

[0012] Step 4: Place the gas diffusion carbon between the microbial reaction system and the photocatalytic water splitting system, wherein the hydrophilic side of the gas diffusion carbon cloth is located on the side of the microbial reaction system, and the strongly hydrophobic side of the gas diffusion carbon cloth is located on the side of the photocatalytic water splitting system. Nitrogen-containing heterocyclic compound wastewater is introduced into the microbial reaction system, and photocatalytic oxygen supply is achieved to enhance microbial degradation by alternating light and dark.

[0013] In step 1, the semiconductor material having the ability of photocatalytic oxygen evolution is a common semiconductor material having the ability of photocatalytic oxygen evolution, such as bismuth vanadate (BiVO4), tungsten trioxide (WO3), graphite carbon nitride (g-C3N4), etc.

[0014] Preferably, in step 1 or 3, the mass concentration of the polytetrafluoroethylene dispersion is 40%-80%.

[0015] Preferably, in step 1, the mass ratio of the polytetrafluoroethylene dispersion to the semiconductor material is 85:15.

[0016] Preferably, in step 1, the mass per unit area of ​​the semiconductor material adhered to the carbon cloth is 2-4 mg / cm 2 .

[0017] In step 2, the hydrophilic material is a common biocompatible hydrophilic material, such as sodium alginate, hydroxylated carbon nanotubes (OH-CNTs), etc.

[0018] Preferably, in step 2, the spin coating speed is 3000 rpm.

[0019] Preferably, in step 3, the heating rate is 2-10° C. / min, and the calcination time is 0.5-2 h.

[0020] Preferably, in step 4, the microbial reaction system comprises simulated wastewater and inoculated sludge; wherein the simulated wastewater is composed of a mixed solution of nitrogen-containing heterocyclic compounds, buffer salts, and trace elements, the carbon and nitrogen elements required for microbial growth metabolism are provided by the nitrogen-containing heterocyclic compounds, and the inoculated sludge is taken from a bioreactor treating wastewater containing nitrogen-containing heterocyclic compounds, and the initial sludge inoculation amount is 6.0-10.0 g L -1 .

[0021] Preferably, in step 4, the composition of the photocatalytic water splitting system includes water. If the semiconductor material used is BiVO4, a strong oxidizing sacrificial agent such as iron nitrate, silver nitrate, etc. needs to be added.

[0022] In step 4, the nitrogen-containing heterocyclic compound is a common nitrogen-containing heterocyclic compound pollutant in organic wastewater, such as N-methylpyrrolidone, pyridine, etc.

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

[0024] (1) The present invention couples photocatalytic technology with biotechnology, strengthens the degradation of nitrogen-containing heterocyclic compound wastewater by microorganisms through photocatalytic oxygen supply, utilizes oxygen-evolving semiconductor materials to decompose water and release oxygen under certain light conditions, and constructs a micro-aerobic / aerobic atmosphere. Since the gas diffusion carbon cloth located on one side of the photocatalytic water decomposition system has the characteristics of strong hydrophobicity, selectivity, and porosity, it can only pass through gas. Therefore, the generated oxygen directly reaches the biological layer in the microbial reaction system (deposited on the hydrophilic side of the gas diffusion carbon cloth), forming an aerobic-anoxic-anaerobic layer microbial layer structure, which is conducive to the in-situ utilization of aerobic microorganisms and the rapid decomposition of organic matter, changes the traditional oxygen supply mode, and improves the utilization rate of O2. After a period of selection, the microbial structure evolves in a direction that is more conducive to the degradation of pollutants, so that the system's tolerance and activity to pollutants are improved, and the system stability is greatly improved, solving the problem of large gas loss and high cost in the traditional aerobic biological treatment of nitrogen-containing heterocyclic compounds;

[0025] (2) The microaerobic / aerobic biological system of photocatalytic semiconductor material oxygen evolution constructed by the present invention promotes the growth of functional microorganisms, strengthens the electron transfer between pollutants and microorganisms, reduces the energy waste and gas pollution caused by the use of mechanical aeration in traditional biodegradation, and is suitable for large-scale industrial applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a schematic diagram of the principle of the photocatalytic semiconductor material decomposition of water and oxygen evolution - microaerobic / aerobic biological system.

[0027] Figure 2 1 is a graph showing the pyridine removal performance of different reaction systems in Example 1. DETAILED DESCRIPTION

[0028] The present invention will be described in detail below in conjunction with specific embodiments and accompanying drawings. The following embodiments are used to illustrate the present invention but are not intended to limit the scope of the present invention.

[0029] The highly hydrophobic and porous W1S1011 carbon cloth used in the following examples was purchased from Rika Hong Kong Co., Ltd.

[0030] Example 1

[0031] A highly hydrophobic and porous W1S1011 carbon cloth was cut into two equal pieces. BiVO4, a photocatalytic oxygen evolution semiconductor material, was bonded to one side of one W1S1011 carbon cloth using a 60wt% polytetrafluoroethylene dispersion. The other W1S1011 carbon cloth was treated with 2.5wt% sodium alginate using a spin coating method (3000 rpm, 0.05-0.2 mL / spray). Finally, the untreated sides of both W1S1011 carbon cloths were bonded together using the same polytetrafluoroethylene dispersion and calcined at 300°C for 30 minutes to produce a gas-diffusion carbon cloth with one hydrophilic and the other strongly hydrophobic. This gas-diffusion carbon cloth is washable, highly biocompatible, contains a photocatalytic material, and exhibits both strong hydrophobic and hydrophilic properties.

[0032] Three groups of reactors were set up: a photocatalytic oxygen evolution bioreactor, a 25°C water bath constant temperature bioreactor, and a water bath control bioreactor. Two sets of light-dark alternation experiments were conducted in each group. The purpose of the light-dark alternation experiment was to compare the effects of light on oxygen production on the microbial reaction system. The constant temperature water bath bioreactor was to eliminate the effects of heat generated by light on the microbial reactor. The settings of each reactor are as follows:

[0033] Photocatalytic oxygen evolution bioreactor: It consists of a microbial reaction system, a gas diffusion carbon cloth and a photocatalytic water splitting system. The gas diffusion carbon is arranged between the microbial reaction system and the photocatalytic water splitting system. The hydrophilic side of the gas diffusion carbon cloth is located on the side of the microbial reaction system, and the strongly hydrophobic side of the gas diffusion carbon cloth is located on the side of the photocatalytic water splitting system. Nitrogen-containing heterocyclic compound wastewater is introduced into the microbial reaction system. The photocatalytic water splitting system consists of water and ferric nitrate. See the schematic diagram. Figure 1 The conditions of the light-dark alternation experiment were: 12 hours of darkness, 3 hours of light, and 9 hours of darkness as one group, with two groups continuously reacting. After multiple measurements, the temperature after 1 hour of light was about 32°C, the temperature after 2 hours of light was about 36°C, and the temperature after 3 hours of light was about 39°C, all within the temperature range where microorganisms can survive. The temperature under dark conditions was 25°C.

[0034] 25℃ water bath constant temperature bioreactor: The structure is the same as the photocatalytic oxygen evolution bioreactor, the water bath temperature is maintained at 25℃, the darkness is maintained for 48 hours, and the temperature is consistent with the setting of the photocatalytic oxygen evolution bioreactor.

[0035] The microbial reaction system of the three reactors was composed of the same amount of simulated wastewater and inoculated sludge. The simulated wastewater was 350 mg / L pyridine solution, 1-4-piperazine diethanesulfonic acid buffer with a pH of 7, and 1 mL L -1 The inoculum sludge was taken from the bioreactor treating pyridine-containing wastewater, and the initial sludge inoculum volume was 8.0 g L -1 .

[0036] Pyridine removal performance of different reaction systems Figure 2 As shown in the figure, it can be seen that the pyridine degradation rate under light conditions in the photocatalytic oxygen evolution reactor is significantly higher than that under dark conditions. Comparison with the water bath control bioreactor and the 25°C water bath constant temperature bioreactor under the same temperature conditions shows that their pyridine degradation rates are relatively slow. It is speculated that the removal of this part of pyridine may be due to the oxygen generated by photocatalysis reaching the microbial layer, facilitating the in-situ utilization of aerobic microorganisms and the rapid decomposition of organic matter, rather than being affected by the increase in temperature. In the photocatalytic oxygen evolution reactor, the pyridine degradation effect gradually decreased in the first few hours after the light was turned off, but it was still higher than the initial dark conditions. This may be because the oxygen has not been completely utilized and is still conducive to the utilization of aerobic microorganisms.

[0037] In the photocatalytic oxygen evolution reactor, the oxygen produced by the photocatalytic decomposition of water by bismuth vanadate is transferred to the biolayer through the medium, forming an aerobic-anoxic-anaerobic biolayer structure, achieving the purpose of microaerobic / aerobic biodegradation of nitrogen-containing heterocyclic compound wastewater. It not only promotes the growth of functional microorganisms and strengthens the electron transfer between pollutants and microorganisms, but also reduces the energy waste and gas pollution caused by the use of mechanical aeration in traditional biodegradation, providing a certain theoretical and practical basis for its application in industry.

[0038] Obviously, the above examples are merely illustrative examples for clarity of explanation and are not intended to limit the embodiments. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all embodiments here. Obvious variations or modifications arising therefrom remain within the scope of protection of the claims of the present invention.

Claims

1. A method for enhancing microbial degradation of nitrogen-containing heterocyclic compound wastewater by photocatalytic oxygen supply, characterized in that: The specific steps are as follows: Step 1: Using a polytetrafluoroethylene dispersion, a semiconductor material having photocatalytic oxygen evolution capability is bonded to one side of a highly hydrophobic and porous carbon cloth; Step 2: Spin coating the hydrophilic material on one side of another piece of highly hydrophobic and porous carbon cloth of the same size; Step 3: Bonding the untreated sides of the two carbon cloths from Step 1 and Step 2 with a polytetrafluoroethylene dispersion, then heating to 200-400° C. and calcining to obtain a gas diffusion carbon cloth with one hydrophilic side and the other strongly hydrophobic side; Step 4: Place the gas diffusion carbon between the microbial reaction system and the photocatalytic water splitting system, wherein the hydrophilic side of the gas diffusion carbon cloth is located on the side of the microbial reaction system, and the strongly hydrophobic side of the gas diffusion carbon cloth is located on the side of the photocatalytic water splitting system. Nitrogen-containing heterocyclic compound wastewater is introduced into the microbial reaction system, and photocatalytic oxygen supply is achieved to enhance microbial degradation by alternating light and dark.

2. The method according to claim 1, characterized in that In step 1, the semiconductor material having the ability of photocatalytic oxygen evolution is selected from bismuth vanadate, tungsten trioxide or graphite carbon nitride.

3. The method according to claim 1, characterized in that In step 1 or 3, the mass concentration of the polytetrafluoroethylene dispersion is 40%-80%.

4. The method according to claim 1, wherein In step 1, the mass ratio of polytetrafluoroethylene dispersion to semiconductor material is 85:15, and the unit area mass of semiconductor material adhered to the carbon cloth is 2-4 mg / cm 2 .

5. The method according to claim 1, wherein In step 2, the hydrophilic material is sodium alginate or hydroxylated carbon nanotubes.

6. The method according to claim 1, wherein In step 2, the spin coating speed is 3000 rpm; in step 3, the heating rate is 2-10°C / min, and the calcination time is 0.5-2 h.

7. The method according to claim 1, wherein In step 4, the microbial reaction system consists of simulated wastewater and inoculated sludge; wherein the simulated wastewater is composed of a mixed solution of nitrogen-containing heterocyclic compounds, buffer salts, and trace elements, and the inoculated sludge is taken from a bioreactor that treats wastewater containing nitrogen-containing heterocyclic compounds, and the initial sludge inoculation volume is 6.0-10.0 gL -1 .

8. The method according to claim 1, characterized in that In step 4, the photocatalytic water splitting system is composed of water, or water and a strong oxidizing sacrificial agent.

9. The method according to claim 8, characterized in that The strong oxidizing sacrificial agent is ferric nitrate or silver nitrate.

10. The method according to claim 1, characterized in that In step 4, the nitrogen-containing heterocyclic compound is N-methylpyrrolidone or pyridine.

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