Method for removing nitrobenzene in wastewater by coupling polypyrrole with sulfur reduction geobacter

Abstract

The invention discloses a method for removing nitrobenzene in wastewater by utilizing polypyrrole coupled sulfur reduction geobacter, which comprises the following steps: mixing polypyrrole, nitrobenzene wastewater and sulfur reduction geobacter, degrading nitrobenzene by utilizing polypyrrole and sulfur reduction geobacter, and adsorbing the degradation product aniline. According to the method for removing the nitrobenzene in the wastewater by coupling the polypyrrole with the sulfur reduction geobacter, under the synergistic effect of the polypyrrole and the sulfur reduction geobacter, the nitrobenzene can be rapidly degraded, meanwhile, the degradation product aniline can be rapidly adsorbed, thorough purification of a water body can be achieved, and the water quality is improved. The method has the advantages of simple process, low cost, good degradation effect, high treatment efficiency and the like, is suitable for rapidly removing the nitrobenzene and the degradation product aniline thereof in the wastewater, is high in use value and good in application prospect, and has important significance in effectively solving the threat of the nitrobenzene and the degradation product aniline thereof to environmental safety and human health.

Description

Technical Field

[0001] The invention belongs to the technical field of environmental materials, and in particular relates to a method for removing nitrobenzene in wastewater by utilizing polypyrrole coupled with Geobacter sulfurreducens. Background Art

[0002] Nitrobenzene is a common nitroaromatic compound. As an inevitable raw material and important product in industrial chemical synthesis, it is widely present in the production processes of medicines, dyes, explosives, etc. Because nitrobenzene is difficult to degrade and highly toxic, it has "triatomic effects" and potential environmental accumulation effects. If nitrobenzene wastewater is discharged directly without treatment, it will pose a serious threat to environmental safety and human health. Traditional wastewater treatment methods based on physical and chemical methods can effectively remove nitrobenzene from wastewater, but there are problems such as high material and reagent costs and the susceptibility to secondary pollution. In contrast, the use of biological methods to remove nitrobenzene from wastewater is a more environmentally friendly treatment method. Among biological methods, electrochemically active bacteria (such as Shewanella and Geobacter sulfurreducens) can achieve nitrobenzene degradation under anaerobic conditions, but have disadvantages such as slow degradation rate and long time consumption, which limits its widespread application. Studies have shown that the use of electron shuttles can improve the electron transfer efficiency of electrochemically active bacteria and accelerate the removal of nitrobenzene. However, existing composite systems composed of electron shuttles and electrochemically active bacteria still struggle to achieve rapid degradation and water purification when used to degrade pollutants. For example, a composite system composed of carbon nanotubes and Shewanella bacteria only removed 94.5% of nitrobenzene after 174 hours, while a system composed of multi-walled carbon nanotubes and Geobacter sulfurreducens required 48 hours to completely remove nitrobenzene. Furthermore, these systems produce aniline as a degradation product after nitrobenzene degradation. Existing solutions do not simultaneously degrade nitrobenzene and remove the aniline degradation product. Although aniline is a low-toxic product, it is also toxic. Therefore, developing a system that can efficiently degrade nitrobenzene while rapidly removing its degradation product, aniline, is of great research value. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to overcome the shortcomings of the existing technology and provide a method for removing nitrobenzene in wastewater by using polypyrrole coupled with Geobacter sulfurreducens, which has simple process, low cost, high treatment efficiency and can simultaneously and quickly remove the degradation product aniline.

[0004] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0005] A method for removing nitrobenzene in wastewater by utilizing polypyrrole coupled with Geobacter sulfurreducens, comprising mixing polypyrrole, nitrobenzene wastewater and Geobacter sulfurreducens, utilizing polypyrrole and Geobacter sulfurreducens to degrade nitrobenzene, and adsorbing the degradation product aniline.

[0006] The above method is further improved and comprises the following steps:

[0007] S1. Mixing polypyrrole, culture medium and nitrobenzene wastewater to obtain a mixed solution; the concentration of polypyrrole in the mixed solution is ≥0.05 g / L;

[0008] S2. Inoculating Geobacter sulfurreducens into the mixed solution in step S1 for cultivation to complete the removal of nitrobenzene in the wastewater.

[0009] The above method is further improved in that, in step S1, the concentration of polypyrrole in the solution is ≥0.10 g / L.

[0010] The above method is further improved in that, in step S1, the concentration of polypyrrole in the solution is ≥0.20 g / L.

[0011] The above method is further improved in that, in step S1, the concentration of polypyrrole in the solution is 0.40 g / L to 0.50 g / L.

[0012] The above method is further improved. In step S1, the polypyrrole is a carbon black-based polypyrrole, and the mass percentage of polypyrrole in the carbon black-based polypyrrole is 20%; the average particle size of the carbon black-based polypyrrole is 100nm to 200nm; the mass percentage of C in the polypyrrole is 92.53%, and the mass percentage of O in the polypyrrole is 6.23%.

[0013] The above method is further improved in that, in step S1, the initial concentration of nitrobenzene in the mixed solution is ≤100 μM.

[0014] The above method is further improved, in step S1, the culture medium is a modified DSMZ culture medium.

[0015] The above method is further improved in that, in step S2, the inoculation amount of the Geobacter sulfurreducens is 1% to 5% of the volume of the mixed solution.

[0016] The above method is further improved, wherein in step S2, the culturing is carried out under anaerobic conditions; a mixed gas of nitrogen and carbon dioxide is introduced during the culturing process to maintain the system in an anaerobic state; the volume ratio of nitrogen to carbon dioxide in the mixed gas of nitrogen and carbon dioxide is 4:1; the culturing is carried out at a temperature of 30°C to 35°C; the rotation speed is controlled at 150 rpm during the culturing process; and the culturing time is 12 hours to 96 hours.

[0017] Compared with the prior art, the advantages of the present invention are:

[0018] (1) In view of the defects of the existing biological degradation system in that it is difficult to quickly degrade nitrobenzene and it is even more difficult to remove the degradation product aniline at the same time, the present invention creatively proposes a method for removing nitrobenzene in wastewater by coupling polypyrrole with sulfur-reducing bacteria, using polypyrrole with high conductivity, strong adsorption performance, good biocompatibility and stable structure as the carrier and electron shuttle of sulfur-reducing bacteria. On the one hand, polypyrrole's good biocompatibility and good binding ability with bacterial cell walls can provide more attachment points for G. sulfurreducens, thereby shortening the transfer distance between the extracellular electrons generated by the metabolism of G. sulfurreducens and nitrobenzene; on the other hand, polypyrrole's excellent adsorption properties can efficiently adsorb nitrobenzene, which not only helps to alleviate the toxic effect of nitrobenzene on G. sulfurreducens in the early stage of the reaction, but also can provide nitrobenzene to G. sulfurreducens through a dynamic adsorption-desorption process, thereby achieving greater mass transfer efficiency and degradation reaction rate; in addition, polypyrrole also has excellent adsorption properties for aniline, and as the amount of polypyrrole increases, the concentration of adsorbed aniline increases accordingly, which is conducive to the rapid enrichment and recovery of aniline during the degradation of nitrobenzene, so as to facilitate further treatment and ultimately achieve the purification of water. Purpose; Furthermore, the excellent electrical conductivity of polypyrrole can promote the rapid transfer of extracellular electrons secreted by G. sulfurreducens to nitrobenzene. Based on this, the composite system constructed by using polypyrrole as a carrier and electron shuttle for G. sulfurreducens exhibits excellent electrochemical performance and electron transfer capacity. It can significantly increase the transfer rate of extracellular electrons secreted by G. sulfurreducens while ensuring good activity of G. sulfurreducens, thereby enabling the rapid transfer of extracellular electrons to nitrobenzene and achieving rapid reduction and degradation of nitrobenzene. More importantly, compared with other carbon materials, polypyrrole has a stable P-π conjugated structure, which obtains good conductivity similar to that of a conductor, and can further accelerate the efficiency of electron transfer. This is an important guarantee for constructing a rapid electron transfer channel and a key means to ensure the efficient degradation of nitrobenzene by the composite system. Moreover, polypyrrole always maintains a stable structure during the process of G. sulfurreducens reducing nitrobenzene and exhibits better electrochemical performance than the original polypyrrole, providing a guarantee for the long-term operation of the composite system. The present invention utilizes polypyrrole coupled with Geobacter sulfurreducens to remove nitrobenzene from wastewater. Under the synergistic action of polypyrrole and Geobacter sulfurreducens, the method can rapidly degrade nitrobenzene and rapidly adsorb the degradation product, aniline, thereby facilitating thorough water purification. The method of the present invention features a simple process, low cost, high treatment efficiency, and excellent degradation effect. It is suitable for rapidly removing nitrobenzene and its degradation product, aniline, from wastewater, has high utility value, promising application prospects, and is of great significance for effectively addressing the threats posed by nitrobenzene and its degradation product, aniline, to environmental safety and human health.

[0019] (2) In the present invention, the use of polypyrrole as an electron shuttle can promote the secretion of more electroactive substances by G. sulfurreducens, further improve the degradation performance of the polypyrrole-coupled G. sulfurreducens system on nitrobenzene, and facilitate the rapid transfer of extracellular electrons of G. sulfurreducens. Polypyrrole neither competes with nitrobenzene for electron acceptors nor produces secondary pollution. Compared with other materials, polypyrrole materials are easy to obtain, easy to recycle, and non-toxic and harmless. They do not undergo morphological changes due to accepting and transferring electrons from G. sulfurreducens. They have a stable structure and are reusable.

[0020] (3) In the present invention, by optimizing the dosage of polypyrrole, the time required for the degradation of nitrobenzene by Geobacter sulfurreducens can be further shortened, and the degradation rate can be further improved while ensuring a good degradation effect. For example, when the concentration of polypyrrole in the mixed system is 0.40 g / L to 0.50 g / L, the effect of polypyrrole coupled with Geobacter sulfurreducens on removing nitrobenzene is optimal, and nitrobenzene can be completely removed within 12 hours. The degradation efficiency is high, the degradation effect is good, and the degradation rate is several times that of the existing technical solutions (for example, it is 5 times the degradation rate of the multi-walled carbon nanotube coupled with Geobacter sulfurreducens system). BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0022] Figure 1 This is a comparison chart of the removal effect of nitrobenzene by Geobacter sulfurreducens under different polypyrrole concentration conditions in Example 1 of the present invention.

[0023] Figure 2 This is a comparison chart of the concentrations of degradation products generated by different concentrations of polypyrrole coupled with Geobacter sulfurreducens in Example 1 of the present invention.

[0024] Figure 3 This is a comparison chart of the removal effects of nitrobenzene by different systems in Example 2 of the present invention.

[0025] Figure 4 This is a comparison chart of the adsorption effects of polypyrrole at different concentrations on nitrobenzene and aniline.

[0026] Figure 5 This is a comparison chart of the adsorption effects of 1.50 g / L polypyrrole and multi-walled carbon nanotubes on nitrobenzene and aniline.

[0027] Figure 6 This is a comparison chart of the removal effects of nitrobenzene by different systems in Example 2 of the present invention.

[0028] Figure 7This is a comparison chart of the concentrations of degradation products generated in different systems in Example 2 of the present invention.

[0029] Figure 8 These are scanning electron microscope (SEM) images of polypyrrole (a), Geobacter sulfurreducens (b), and the polypyrrole-coupled Geobacter sulfurreducens complex system (cd) in Example 2 of the present invention.

[0030] Figure 9 1 is the X-ray diffraction (XRD) spectrum of the original polypyrrole and the polypyrrole in the coupled system in Example 2 of the present invention.

[0031] Figure 10 1s spectra of the original polypyrrole and the polypyrrole in the coupled system in Example 2 of the present invention.

[0032] Figure 11 This is the XPS N1s spectrum of the original polypyrrole and the polypyrrole in the coupled system in Example 2 of the present invention.

[0033] Figure 12 Electrochemical cyclic voltammetry (CV) diagrams of different systems in Example 2 of the present invention.

[0034] Figure 13 The electrochemical cyclic voltammetry diagrams of the supernatants of different systems in Example 2 of the present invention are shown.

[0035] Figure 14 This is a diagram showing the removal effect of p-nitrobenzene by manganese dioxide and Geobacter sulfurreducens in combination with the degradation product aniline in Comparative Example 1.

[0036] Figure 15 This is a diagram showing the removal effect of humic acid and Geobacter sulfurreducens combined with p-nitrobenzene in Comparative Example 2 and the generated concentration of the degradation product aniline. DETAILED DESCRIPTION

[0037] The present invention will be further described below in conjunction with the accompanying drawings and specific preferred embodiments, but the scope of protection of the present invention is not limited thereby.

[0038] In the following examples of the present invention, unless otherwise specified, the materials and instruments used are commercially available, the equipment used is conventional equipment, and the data obtained are the average values ​​of more than three repeated experiments.

[0039] Example 1:

[0040] A method for removing nitrobenzene from wastewater using polypyrrole coupled with Geobacter sulfurreducens, specifically comprising: mixing polypyrrole and nitrobenzene wastewater with Geobacter sulfurreducens, degrading nitrobenzene using polypyrrole and Geobacter sulfurreducens, and adsorbing the degradation product aniline, including the following steps:

[0041] In a 125 mL serum bottle, 0.05 g / L to 0.50 g / L of polypyrrole (Pyy) was added to 100 mL of modified DSMZ medium (conventional culture medium). Nitrobenzene wastewater was also added to achieve a nitrobenzene concentration of 100 μM in the system. The PCA strain of Geobacter sulfurreducens (G. sulfurreducens) was inoculated at an inoculum size of 2% of the culture medium system. The system was maintained in an anaerobic state using a mixture of nitrogen and carbon dioxide in a volume ratio of 4:1. The culture was carried out at a temperature of 30°C and a rotation speed of 150 rpm for 72 h to degrade the nitrobenzene in the system.

[0042] In this embodiment, the polypyrrole used is carbon black-based polypyrrole, that is, polypyrrole is loaded on carbon black, wherein the mass percentage of polypyrrole is 20%, the average particle size is 100nm~200nm, and the mass percentage of C in the polypyrrole is 92.53%, and the mass percentage of O is 6.23%.

[0043] The carbon black-based polypyrrole used in this embodiment is a commercially available product. Using carbon black as a carrier can make the polypyrrole more uniform, which is beneficial for the polypyrrole to maintain a larger specific surface area and thus maintain its extremely strong adsorption performance.

[0044] The residual concentration of the pollutant nitrobenzene and the corresponding concentration of the reduced product aniline were determined. The results were as follows: Figure 1 as well as Figure 2 shown.

[0045] Figure 1 This is a comparison chart of the removal effects of nitrobenzene by the polypyrrole-coupled Geobacter sulfurreducens system with different concentrations in Example 1 of the present invention. Figure 2 This is a comparison chart of the generated concentrations of aniline, a degradation product, in the system of polypyrrole coupled with Geobacter sulfurreducens at different concentrations in Example 1 of the present invention. Figure 1 and Figure 2 In the figure, the solid line represents the 0.05 g / L polypyrrole-coupled Geobacter sulfurreducens PCA strain system (Pyy-PCA), the dashed line represents the 0.10 g / L polypyrrole-coupled Geobacter sulfurreducens PCA strain system, the dotted line represents the 0.20 g / L polypyrrole-coupled Geobacter sulfurreducens PCA strain system, the short dashed line represents the 0.40 g / L polypyrrole-coupled Geobacter sulfurreducens PCA strain system, and the short dotted line represents the 0.50 g / L polypyrrole-coupled Geobacter sulfurreducens PCA strain system.

[0046] Depend on Figure 1 It can be seen that when the concentration of polypyrrole is 0.05g / L~0.50g / L, the composite system formed by polypyrrole coupled with Geobacter sulfurreducens can effectively remove nitrobenzene within 24h, and when the polypyrrole concentration is 0.40g / L and 0.50g / L, nitrobenzene can be completely removed by the polypyrrole coupled with Geobacter sulfurreducens composite system within 12h.

[0047] Depend on Figure 2 It can be seen that when the concentration of polypyrrole material is 0.05 g / L, 0.10 g / L, 0.20 g / L, 0.40 g / L and 0.50 g / L, the production rate of aniline, the degradation product generated by the composite system formed by polypyrrole coupled with Geobacter sulfurreducens when degrading nitrobenzene, is 88.99%, 90.41%, 88.49%, 84.52% and 85.79% respectively.

[0048] This indicates that optimizing the polypyrrole dosage can further shorten the time required for G. sulfurreducens to degrade nitrobenzene, further increasing the degradation rate while ensuring good degradation results. For example, when the polypyrrole concentration in the composite system was 0.40 g / L and 0.50 g / L, polypyrrole-coupled G. sulfurreducens achieved optimal nitrobenzene removal, achieving complete removal of p-nitrobenzene within 12 hours with high degradation efficiency and good degradation results. When conventional biochar (such as sludge biochar) was used in place of polypyrrole, the resulting composite system required 15 days to completely remove 100 μM nitrobenzene. A multi-walled carbon nanotube-coupled G. sulfurreducens system also required 48 hours to complete p-nitrobenzene degradation. In comparison, the polypyrrole-coupled G. sulfurreducens system significantly improved its p-nitrobenzene degradation efficiency.

[0049] In order to make a more intuitive comparison, a comparative experiment was conducted. 100 μM nitrobenzene was degraded by 0.50 g / L polypyrrole coupled with Geobacter sulfurreducens system, and 200 μM nitrobenzene was degraded by 1.5 g / L multi-walled carbon nanotube coupled with Geobacter sulfurreducens system (CNTs-PCA). The first-order kinetic curves of the two degradation systems were drawn. The results are shown in the figure. Figure 3 shown. Figure 3 The first-order kinetic curves of nitrobenzene degradation by the two systems show that the first-order kinetic constant for treating 200 μM nitrobenzene wastewater with 1.50 g / L CNTs-PCA is 0.050, and the first-order kinetic constant for treating 100 μM nitrobenzene wastewater with 0.50 g / L Pyy-PCA is 0.254, which is about 5 times that of the former. This fully proves that the degradation rate of nitrobenzene by the polypyrrole-coupled Geobacter sulfurreducens system is significantly better than that by the multi-walled carbon nanotube-coupled Geobacter sulfurreducens system.

[0050] Study on the Adsorption Performance of Polypyrrole on Aniline, a Degradation Product of Nitrobenzene

[0051] The production rate of aniline, a degradation product of nitrobenzene, generated by the composite system formed by polypyrrole coupled with Geobacter sulfurreducens, gradually decreased with the increase of polypyrrole dosage. Figure 2 As shown, this is because polypyrrole also has excellent adsorption properties for aniline, which is conducive to the rapid enrichment and recovery of aniline during the degradation of nitrobenzene, so as to facilitate further treatment and ultimately achieve the purpose of purifying water.

[0052] Polypyrrole not only has a good adsorption effect on nitrobenzene, but also has a good adsorption effect on aniline, and the adsorption amount increases with the increase of polypyrrole dosage, such as Figure 4 As shown, Figure 4 This is a comparison chart of the adsorption effects of polypyrrole of different concentrations on nitrobenzene and aniline. The figure shows that the higher the concentration of polypyrrole, the stronger the adsorption of nitrobenzene and aniline.

[0053] In the study, the inventors of this application found that sludge biochar, graphene oxide, and reduced graphene oxide could not adsorb aniline. Multi-walled carbon nanotubes also had good adsorption performance for nitrobenzene, but had very limited adsorption for aniline. Figure 5 As shown, Figure 5 This is a comparison of the adsorption effects of 1.50g / L polypyrrole and 1.50g / L multi-walled carbon nanotubes on nitrobenzene and aniline, respectively. Figure 5 It can be seen that 1.50g / L polypyrrole and 1.50g / L multi-walled carbon nanotubes have similar nitrobenzene adsorption effects. The two can make the residual nitrobenzene concentration similar after adsorption for 120 minutes in a nitrobenzene solution with an initial concentration of 200μM. However, when the same conditions are used to adsorb aniline, multi-walled carbon nanotubes can only adsorb about 15%, while polypyrrole's adsorption of aniline is greater than 50%. This shows that polypyrrole has stronger aniline adsorption performance than multi-walled carbon nanotubes, and the adsorption speed is faster. It can adsorb 40% aniline in 5 minutes. Therefore, polypyrrole has the application potential of quickly adsorbing aniline from water bodies after synergistically degrading nitrobenzene with Geobacter sulfurreducens. Figure 2 、 Figure 4 and Figure 5 It can be seen that the addition of excessive polypyrrole-Geobacter sulfurreducens preparation is beneficial to the adsorption and degradation of nitrobenzene while removing the degradation product aniline in water.

[0054] Example 2

[0055] A method for removing nitrobenzene from wastewater using polypyrrole coupled with Geobacter sulfurreducens, specifically comprising: mixing polypyrrole and nitrobenzene wastewater with Geobacter sulfurreducens, degrading nitrobenzene using polypyrrole and Geobacter sulfurreducens, and adsorbing the degradation product aniline, including the following steps:

[0056] In a 125 mL serum bottle, 0.50 g / L polypyrrole was added to 100 mL of modified DSMZ culture medium, and nitrobenzene wastewater was added at the same time to make the nitrobenzene concentration in the system 100 μM. The PCA strain of Geobacter sulfurreducens was inoculated at an inoculum size of 2% of the culture medium system. A mixed gas of nitrogen and carbon dioxide with a volume ratio of 4:1 was used to maintain the system in an anaerobic state. The system was cultured at a temperature of 30°C and a rotation speed of 150 rpm for 72 hours to degrade the nitrobenzene in the system.

[0057] In this embodiment, the polypyrrole used is carbon black-based polypyrrole, that is, polypyrrole is loaded on carbon black, wherein the mass percentage of polypyrrole is 20%, the average particle size is 100nm~200nm, and the mass percentage of C in the polypyrrole is 92.53%, and the mass percentage of O is 6.23%.

[0058] The carbon black-based polypyrrole used in this embodiment is a commercially available product. Using carbon black as a carrier can make the polypyrrole more uniform, which is beneficial for the polypyrrole to maintain a larger specific surface area and thus maintain its extremely strong adsorption performance.

[0059] Blank group: blank control, without adding Geobacter sulfurreducens and polypyrrole, and other conditions are the same as Example 2.

[0060] Control group 1: Pyy, only 0.50 g / L polypyrrole was added, and other conditions were the same as those in Example 2.

[0061] Control group 2: PCA, only 2% of the culture volume of Geobacter sulfurreducens was added, and other conditions were the same as those in Example 2.

[0062] The concentration changes of nitrobenzene pollutants and the concentration changes of aniline generated by degradation in different systems were measured. The results were as follows: Figure 6 and Figure 7 shown.

[0063] Figure 6 This is a comparison chart of the removal effects of nitrobenzene by different systems in Example 2 of the present invention. Figure 7 This is a comparison chart of the concentrations of degradation products produced in different systems in Example 2 of the present invention. Figure 6 and Figure 7 In the figure, the solid line represents the blank control, the dashed line represents the Geobacter sulfurreducens PCA, the dashed line represents polypyrrole Pyy, and the dotted line represents the polypyrrole-coupled Geobacter sulfurreducens system Pyy-PCA.

[0064] Depend on Figure 6 and Figure 7It can be seen that the composite system formed by polypyrrole coupling with G. sulfurreducens in the present invention can rapidly degrade nitrobenzene, and the generation rate of aniline in the mixed solution can reach up to 92.36%. Other systems have difficulty achieving the same degradation effect. Among them, polypyrrole only has an adsorption effect on nitrobenzene, but no degradation effect; G. sulfurreducens only shows a degradation effect of 14.25% in wastewater containing 100 μM nitrobenzene. This shows that the addition of polypyrrole is conducive to the efficient removal of nitrobenzene by G. sulfurreducens, mainly through the following pathways: polypyrrole first adsorbs nitrobenzene pollutants and provides attachment sites for G. sulfurreducens. G. sulfurreducens transfers the electrons generated by metabolism to polypyrrole, and then uses the excellent conductive properties of polypyrrole to transfer electrons to nitrobenzene, thereby achieving rapid and complete removal of nitrobenzene.

[0065] Figure 8 The SEM images of polypyrrole (a), Geobacter sulfurreducens (b) and polypyrrole coupled Geobacter sulfurreducens complex system (cd) in Example 2 of the present invention are shown. Figure 8 As can be seen, polypyrrole is a relatively uniform, round particle, while G. sulfurreducens cells are rod-shaped with blunt, rounded ends. In the polypyrrole-coupled G. sulfurreducens complex, most G. sulfurreducens cells adhere to the material surface, while a few are interspersed within the polypyrrole or encapsulated by it. This indicates that polypyrrole provides a favorable growth environment for G. sulfurreducens, and the resulting dense complex provides a preliminary foundation for shortening the distance of extracellular electron transfer.

[0066] Figure 9 The XRD spectra of polypyrrole and polypyrrole in the coupling system in Example 2 of the present invention are shown in FIG. Figure 9 It can be seen that the structure of polypyrrole did not change significantly before and after the cooperative reaction with Geobacter sulfurreducens to degrade nitrobenzene, and both showed a characteristic peak of broad diffraction at 25°.

[0067] Figure 10 The XPS C1s spectra of polypyrrole and polypyrrole in the coupled system in Example 2 of the present invention are shown in FIG. Figure 10 It can be seen that polypyrrole has a P-π conjugated structure, which makes it have good electrical conductivity similar to that of a conductor. After polypyrrole cooperates with Geobacter sulfurreducens to degrade nitrobenzene, the content of α-carbon atoms (CC, CH or C=C) decreases from 56.49% to 52.79%, which indicates that there is a small amount of breakage in the reversible redox process of polypyrrole. In addition, the carbon-nitrogen bond (C=N, CN + ) content increased from 35.10% to 38.80%, demonstrating the good biocompatibility and binding ability of polypyrrole to microbial cells. The carbon-containing functional groups of polypyrrole did not undergo significant changes before and after the synergistic reaction with Geobacter sulfurreducens to degrade nitrobenzene, ensuring the continuous operation of the polypyrrole-coupled Geobacter sulfurreducens system for nitrobenzene removal from wastewater.

[0068] Figure 11 The XPS N1s spectra of polypyrrole and polypyrrole in the coupled system in Example 2 of the present invention are shown in FIG. Figure 11 It can be seen that polypyrrole contains abundant monopoles (-NH ·+ -) and bipolaron (=NH + -) form, which is the source of its excellent conductivity. After polypyrrole collaborated with Geobacter sulfurreducens to degrade nitrobenzene, the monopolaron content dropped from 65.71% to 8.82%, indicating that Geobacter sulfurreducens tightly binds to polypyrrole. Electrons generated by its metabolism are first transferred to polypyrrole, and then from polypyrrole to the electron acceptor, nitrobenzene. Once the nitrobenzene degradation reaction ceases, polypyrrole serves only as an electron acceptor and no longer transfers electrons.

[0069] Figure 12 The CV graphs of different systems in Example 2 of the present invention are shown in the figure. The electrochemical test results of each sample in Example 2 at the initial stage and after 12 hours of reaction are shown in the figure. Figure 12 It can be seen that through electrochemical characterization tests, it was verified that polypyrrole has excellent electrochemical properties, and this performance was further optimized by Geobacter sulfurreducens.

[0070] In the coupled system, polypyrrole acts as an electron shuttle, and its electrical conductivity is the primary source of its activity. Having established that polypyrrole promotes nitrobenzene removal by PCA strains, the strength of its electrical conductivity can, to some extent, indicate the magnitude of its beneficial effect. In this study, we conducted comparative tests of polypyrrole and multi-walled carbon nanotubes (MWCNTs) and found that the electrical conductivity of both polypyrrole and MWCNTs was enhanced by PCA. A concentration of 0.50 g / L polypyrrole exhibited a similar maximum response current intensity and area as that of 1.50 g / L MWCNTs. At the same concentration, polypyrrole exhibited stronger electrical conductivity than MWCNTs.

[0071] In addition, the samples and control samples after the reaction in this embodiment were centrifuged and filtered to remove polypyrrole and bacteria to obtain supernatants, and the supernatants were subjected to electrochemical tests. The results are as follows: Figure 13 As shown, Figure 13Figures 2A and 2B are electrochemical cyclic voltammetry diagrams of different systems in Example 2 of the present invention. As can be seen from the figure, the conductivity of the supernatant after the reaction of PCA + 0.5 g / L Pyy is significantly enhanced compared to PCA alone and 0.5 g / L Pyy alone. In previously studied materials (including multi-walled carbon nanotubes), it is common for electrochemically active bacteria to exhibit better conductivity than pure electrochemically active bacteria after combining with materials. However, no enhanced conductivity of the supernatant was observed. We speculate that polypyrrole may promote the secretion of more electroactive substances by Geobacter sulfurreducens, resulting in enhanced conductivity of the supernatant. This is also an important reason why the polypyrrole-coupled Geobacter sulfurreducens system is superior to other material-coupled systems.

[0072] In this example, SEM, XRD, XPS, electrochemical characterization and other means were used to determine the efficiency and stability of the composite system formed by polypyrrole coupled with Geobacter sulfurreducens in removing nitrobenzene from wastewater, and the composite system is suitable for removing nitrobenzene, a difficult-to-degrade organic matter, from wastewater.

[0073] Investigation of different electron shuttles

[0074] In the early stages of building the system, we conducted experimental research on different types of conductive materials. Two typical representative materials are listed below.

[0075] Comparative Example 1:

[0076] First, the electron shuttle must not be a strong oxidant, producing oxygen either spontaneously or through bacterial action. Strong oxidants can kill bacteria, and Geobacter sulfurreducens is a strictly anaerobic bacterium, so the production of oxygen can reduce the pollutant removal rate. The electron shuttle should act as an intermediate mediator of electrons rather than a final receiver. Based on the idea that Geobacter sulfurreducens reduces ferric iron to ferrous iron, which then reduces nitrobenzene, this comparative example uses manganese dioxide and Geobacter sulfurreducens to degrade nitrobenzene.

[0077] The experimental process of this comparative example is basically the same as that of Example 1, except that manganese dioxide is used instead of polypyrrole. The concentrations of manganese dioxide are 0.02 g / L, 0.06 g / L, 0.10 g / L, 0.15 g / L and 0.20 g / L respectively. The results are shown in FIG. Figure 14 As shown, Figure 14 The graphs showing the removal effect of p-nitrobenzene by manganese dioxide and Geobacter sulfurreducens and the concentration of the degradation product aniline are shown respectively. Figure 14As can be seen from the results, the removal rate of nitrobenzene with an initial concentration of 100 μM by this system in 72 h was less than 50%. The degradation effect of the sample with manganese dioxide on nitrobenzene was even worse than that with PCA alone. This is because manganese dioxide will be reduced by the action of Geobacter sulfurreducens, but it will become a competitive electron acceptor for nitrobenzene, only accepting electrons without transferring them to nitrobenzene. In addition, it does not have the ability to adsorb and degrade nitrobenzene, and instead hinders the removal of nitrobenzene. Therefore, manganese dioxide, which competes with nitrobenzene for electron acceptors, cannot be used in the solution of the present invention.

[0078] Comparative Example 2:

[0079] The electron shuttle is preferably reusable and does not cause secondary pollution. Humic acid (HA) has also been shown to be able to act as an electron shuttle. In this comparative example, humic acid and Geobacter sulfurreducens were used to degrade nitrobenzene.

[0080] The experimental process is basically the same as that of Example 1, with the main difference being that humic acid is used instead of polypyrrole. The concentrations of humic acid are 0.005 g / L, 0.010 g / L, 0.020 g / L, 0.040 g / L and 0.050 g / L, respectively. The results are shown in FIG. Figure 15 As shown, Figure 15 The graphs show the removal effect of humic acid and Geobacter sulfurreducens combined with p-nitrobenzene and the concentration of the degradation product aniline. Figure 15 It can be seen that the use of 0.050g / L humic acid in combination with PCA can completely degrade nitrobenzene with an initial concentration of 100μM within 24 hours, and the degradation effect is good. However, it was found in the experimental study that humic acid is soluble in water and cannot be separated and reused. Figure 15 As shown in (b), in the humic acid-PCA degradation system at 0.040 g / L and 0.050 g / L, the concentration of the degradation product aniline was surprisingly much higher than the initial concentration of nitrobenzene, indicating that humic acid and Geobacter sulfurreducens may have undergone other reactions, producing some other organic matter, causing the instrument to measure excessive substances in the original spectral band. Therefore, using humic acid as an electron shuttle to accelerate the removal of nitrobenzene by Geobacter sulfurreducens, although also having a good degradation effect, is difficult to recycle and may also cause secondary pollution. In contrast, polypyrrole is insoluble in water and non-toxic. Experimental studies have found that it does not undergo morphological changes due to accepting and transmitting electrons from Geobacter sulfurreducens, and is reusable.

[0081] It can be seen from the above results that, compared with conventional methods, the method proposed in the present invention for removing nitrobenzene in wastewater by coupling polypyrrole with sulfur-reducing bacteria uses polypyrrole with high conductivity, strong adsorption performance, good biocompatibility and stable structure as a carrier and electron shuttle of sulfur-reducing bacteria. On the one hand, by utilizing the good biocompatibility and good binding ability of polypyrrole with the bacterial cell wall, it can provide more attachment points for sulfur-reducing bacteria, thereby facilitating shortening the transfer distance between the extracellular electrons generated by the metabolism of sulfur-reducing bacteria and nitrobenzene; on the other hand, by utilizing the excellent adsorption performance of polypyrrole, it can efficiently adsorb nitrobenzene, which is not only conducive to alleviating the toxic effect of nitrobenzene on sulfur-reducing bacteria in the early stage of the reaction, but also can provide nitrobenzene to sulfur-reducing bacteria through a dynamic adsorption-desorption process, thereby achieving greater mass transfer efficiency and degradation reaction rate; in addition, polypyrrole also has excellent adsorption performance for aniline, and as the amount of polypyrrole increases, the concentration of adsorbed aniline increases accordingly, which is conducive to achieving rapid enrichment and recovery of aniline during the degradation of nitrobenzene, so as to facilitate further treatment and ultimately achieve the purification of water bodies. Purpose; Furthermore, the excellent electrical conductivity of polypyrrole can promote the rapid transfer of extracellular electrons secreted by G. sulfurreducens to nitrobenzene. Based on this, the composite system constructed by using polypyrrole as a carrier and electron shuttle for G. sulfurreducens exhibits excellent electrochemical performance and electron transfer capacity. It can significantly increase the transfer rate of extracellular electrons secreted by G. sulfurreducens while ensuring good activity of G. sulfurreducens, thereby enabling the rapid transfer of extracellular electrons to nitrobenzene and achieving rapid reduction and degradation of nitrobenzene. More importantly, compared with other carbon materials, polypyrrole has a stable P-π conjugated structure, which obtains good conductivity similar to that of a conductor, and can further accelerate the efficiency of electron transfer. This is an important guarantee for constructing a rapid electron transfer channel and a key means to ensure the efficient degradation of nitrobenzene by the composite system. Moreover, polypyrrole always maintains a stable structure during the process of G. sulfurreducens reducing nitrobenzene and exhibits better electrochemical performance than the original polypyrrole, providing a guarantee for the long-term operation of the composite system. The method of the present invention utilizes polypyrrole coupled with Geobacter sulfurreducens to remove nitrobenzene in wastewater. Under the synergistic action of polypyrrole and Geobacter sulfurreducens, rapid degradation of nitrobenzene can be achieved. The method has the advantages of simple process, low cost, high treatment efficiency, good degradation effect, etc. The method is suitable for rapidly removing nitrobenzene in wastewater and can also rapidly adsorb the degradation product aniline, thereby facilitating thorough purification of water bodies. The method has high use value and good application prospects.

[0082] The above embodiments are merely preferred embodiments of the present invention, and the scope of protection of the present invention is not limited to the above embodiments. All technical solutions that fall within the scope of protection of the present invention are within the scope of protection of the present invention. It should be noted that improvements and modifications that can be made by a person skilled in the art without departing from the principles of the present invention are also considered to be within the scope of protection of the present invention.

Claims

1. A method for removing nitrobenzene from wastewater using polypyrrole coupled with Geobacter sulfurreducens, characterized in that: The method comprises the following steps: mixing polypyrrole and nitrobenzene wastewater with Geobacter sulfurreducens, utilizing polypyrrole and Geobacter sulfurreducens to synergistically degrade nitrobenzene, and adsorbing the degradation product aniline.

2. The method according to claim 1, characterized in that The following steps are involved: S1. Mixing polypyrrole, culture medium and nitrobenzene wastewater to obtain a mixed solution; the concentration of polypyrrole in the mixed solution is ≥0.05 g / L; S2. Inoculating Geobacter sulfurreducens into the mixed solution in step S1 for cultivation to complete the removal of nitrobenzene in the wastewater.

3. The method according to claim 2, characterized in that In step S1, the concentration of polypyrrole in the solution is ≥0.10 g / L.

4. The method according to claim 3, characterized in that In step S1, the concentration of polypyrrole in the solution is ≥0.20 g / L.

5. The method according to claim 4, characterized in that In step S1, the concentration of polypyrrole in the solution is 0.40 g / L to 0.50 g / L.

6. The method according to claim 1, characterized in that In step S1, the polypyrrole is a carbon black-based polypyrrole, and the mass percentage of polypyrrole in the carbon black-based polypyrrole is 20%; the average particle size of the carbon black-based polypyrrole is 100nm to 200nm; the mass percentage of C in the polypyrrole is 92.53%, and the mass percentage of O in the polypyrrole is 6.23%.

7. The method according to any one of claims 2 to 6, characterized in that: In step S1, the initial concentration of nitrobenzene in the mixed solution is ≤100 μM.

8. The method according to any one of claims 2 to 6, characterized in that: In step S1, the culture medium is a modified DSMZ culture medium.

9. The method according to any one of claims 2 to 6, characterized in that: In step S2, the inoculation amount of the Geobacter sulfurreducens is 1% to 5% of the volume of the mixed solution.

10. The method according to any one of claims 2 to 6, characterized in that: In step S2, the culture is carried out under anaerobic conditions; a mixed gas of nitrogen and carbon dioxide is introduced during the culture process to maintain the system in an anaerobic state; the volume ratio of nitrogen to carbon dioxide in the mixed gas of nitrogen and carbon dioxide is 4:1; the culture is carried out at a temperature of 30°C to 35°C; the rotation speed is controlled at 150 rpm during the culture process; and the culture time is 12 hours to 96 hours.

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