A tannin-modified iron-biochar composite conductive carrier material and a preparation method and application thereof

Abstract

The present application belongs to the field of environmental remediation and pollution control technology, and particularly relates to a tannin acid modified iron-biochar composite conductive carrier material and a preparation method and application thereof. The tannin acid modified iron-biochar composite conductive carrier is prepared by a simple low-temperature hydrothermal synthesis method, has low raw material cost, simple method, good conductivity, recyclability and high stability; the prepared tannin acid modified iron-biochar novel conductive carrier can store and release electrons, enhance direct interspecies electron transfer between acid-producing bacteria and methanogens in the anaerobic treatment process, and carbon felt immobilization is conducive to the formation of biofilm, which not only solves the problem of recovery of conductive materials, but also significantly improves the methane production.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of environmental remediation and pollution control, and particularly relates to a tannin acid modified iron-biochar composite conductive carrier material and a preparation method and application thereof. BACKGROUND

[0002] Environmental pollution and energy shortage restrict the development of global economy. Anaerobic wastewater treatment is a very promising technology to solve these two problems, because it can recover energy (such as methane) from organic pollutants. However, the performance of methanogenesis in anaerobic systems is greatly affected by complex interspecies interactions and low electron transfer rates between acid-producing bacteria and methanogens. Therefore, enhancing electron transfer, promoting microbial metabolism and improving anaerobic methanogenic performance through various regulation strategies have become a research hotspot.

[0003] In recent years, more and more carbon-based and iron-based conductive materials (such as activated carbon, graphene, Fe3O4, ZVI) are used to promote the process of direct interspecies electron transfer (DIET) in anaerobic digestion. Carbon-based conductive materials have large surface area and high stability and conductivity, which provide a favorable environment for the growth of microorganisms. However, due to the small number of electron transfer sites on the material surface, the electron transfer between the cell surface and the carbon-based conductive material is limited, and the direct use of carbon-based conductive materials to improve the methanogenic capacity of anaerobic systems is limited. Fe can be used as an active site for carbon-based conductive materials to enhance the conductivity of carbon-based conductive materials. The introduction of iron into carbon-based conductive materials is expected to improve their electron transfer capacity and promote the improvement of methane production in anaerobic treatment processes.

[0004] However, the composite conductive materials used in anaerobic systems usually require a tedious preparation process, high preparation cost and are difficult to recover, and potential biological toxicity and environmental risk cannot be ignored, which greatly limits their engineering application.

[0005] Therefore, how to provide a green synthesis method to prepare a new type of composite conductive carrier material is a technical problem to be solved by those skilled in the art. SUMMARY

[0006] Therefore, the present application discloses a tannin acid modified iron-biochar composite conductive carrier material and a preparation method and application thereof. By using a green synthesis method to prepare a new type of composite conductive carrier, the problem of recycling of conductive materials in anaerobic systems is solved, the methane production is improved, and the microbial metabolism and direct interspecies electron transfer process are accelerated.

[0007] It should be noted that tannic acid (TA) as a biodegradable natural plant polyphenol has excellent metal chelation and electron transfer performance, and its aromatic and quinone groups may also affect the anaerobic treatment process. Low-temperature heat treatment can maximize the retention of oxygen-containing functional groups in tannic acid-iron complexes, improve the redox activity, and promote electron transfer. Iron and TA form stable complexes under neutral or slightly alkaline conditions. In the preparation process, the conductive carrier carbon felt (CF) is introduced, and the in-situ growth of the conductive composite on the carrier is promoted by one-pot hydrothermal method, which has the advantages of promoting mass transfer, reducing internal resistance and enhancing microbial adhesion. At the same time, the green synthesis of plant polyphenols is more environmentally friendly and has lower cost, and the strengthening effect on anaerobic wastewater treatment is more persistent and stable than single carrier or iron / carbon material. Therefore, the present application uses low-temperature heat treatment of tannic acid to prepare a new green Fe-TA-C composite conductive carrier to strengthen the direct interspecies electron transfer (DIET) in anaerobic process, which is a promising strategy.

[0008] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0009] The first object of the present application is to provide a preparation method of tannic acid modified iron-biochar composite conductive carrier material, which specifically comprises the following steps:

[0010] (1) Biochar is obtained by calcining wood raw materials at high temperature, and then washed alternately with deionized water and ethanol after natural cooling, and dried and sieved for use;

[0011] It should be noted that biochar prepared from waste raw materials is an environmentally friendly medium, and its rich porous structure provides more favorable conditions for microbial adhesion and provides good active sites for electron transfer in anaerobic systems.

[0012] (2) The biochar obtained in step (1) and soluble iron salt are dissolved in deionized water and magnetically stirred for 30-40 min;

[0013] It should be noted that the conductivity of biochar is improved by doping a small amount of iron.

[0014] (3) After complete dissolution, tannic acid (TA) is added and stirred for 6-8 h, and the pH value of the obtained mixed solution is adjusted to 7-9 by using NaOH or KOH;

[0015] It should be noted that tannic acid (TA) can be tightly combined with carbon substrates through hydrogen bond interaction, and tannic acid and iron form stable complexes under neutral or slightly alkaline conditions, which promotes the electron transfer between microorganisms and exogenous electron acceptors. Long-term stirring can promote the reaction of tannic acid and iron.

[0016] (4) The mixed solution in step (3) is transferred into a reaction kettle together with the pretreated carbon felt for hydrothermal synthesis, and after natural cooling, the product is washed with deionized water and vacuum dried to obtain the tannic acid modified iron-biochar composite conductive carrier material.

[0017] It should be noted that the present application forms a conductive composite carrier by hydrothermal synthesis of primary growth Fe-TA-C composite material, which has the advantages of large surface area, strong conductivity and good chemical stability. On the one hand, it can be used as a fixed carrier without loss, avoiding the problem of powder material recovery and the influence on the subsequent process, and has certain economic feasibility. On the other hand, it can induce microorganisms to form functional biofilm, strengthen direct interspecies electron transfer DIET in anaerobic process, and ultimately improve the methanogenic performance, realizing efficient energy recovery.

[0018] Optionally, in step (1), the biochar is wood biochar, the calcination temperature is 450-550℃, the calcination time is 1-3h, the heating rate is 5-10℃ / min, the biochar is washed with deionized water and ethanol alternately for 3-4 times, dried at 60-65℃, the drying time is 8-12h, and the powder with a mesh size of 100-150 is obtained for use.

[0019] Optionally, in step (2), 0.50-1.0g of biochar and 0.02-0.05g of soluble iron salt are added to 40-50mL of deionized water; the soluble iron salt is preferably FeCl3·6H2O or Fe(NO3)3·6H2O.

[0020] Optionally, in step (3), 0.04-0.32g of tannic acid is added, the molar ratio of tannic acid to iron is 1:1-1:3, and 0.1-0.2M NaOH or KOH solution is added dropwise until the pH of the mixed solution is 7-9.

[0021] Optionally, in step (4), the pretreatment method of the carbon felt is as follows: 2-5×2-5×0.1-0.2cm 3 of carbon felt is soaked in 30% hydrogen peroxide solution at 80-90℃ water bath for 1-2h; washed with deionized water to neutral pH, dried in an oven at 60-65℃ for 3-6h to obtain the pretreated carbon felt. The carbon felt carries hydroxyl groups, increases the proportion of oxygen-containing functional groups, better combines with TA, strengthens the redox capacity of the composite conductive carrier material, and promotes electron transfer.

[0022] Further, in step (4), the hydrothermal temperature is 120-140℃, the hydrothermal synthesis time is 12-16h, the product is washed with deionized water for 3-4 times after natural cooling to below 60℃, the vacuum drying temperature is 60-65℃, and the drying time is 8-12h.

[0023] The second object of the present application is to provide a tannic acid modified iron-biochar composite conductive carrier material prepared by the method as described above, which is a Fe-TA-C composite conductive carrier material that promotes electron transfer.

[0024] The third object of the present application is to provide an application of the tannic acid modified iron-biochar composite conductive carrier material prepared by the method as described above in environmental remediation and pollution control technology.

[0025] Further, the application of the tannic acid modified iron-biochar composite conductive carrier material in anaerobic treatment of waste water can be applied to municipal sewage, industrial waste water, aquaculture waste water and other scenarios.

[0026] Specifically, anaerobic sludge and tannic acid modified iron-biochar composite material / carrier are placed in an anaerobic reactor, the wastewater to be treated is introduced, and mixed culture is carried out for 10-12 days to biodegrade organic pollutants, the pH is maintained at 7.0-8.5, and the hydraulic retention time is 12h. The anaerobic sludge concentration is 5-6gVSS / L; the composite material / carrier addition amount is 0.05-0.1g / L; the anaerobic reactor includes intermittent flow, semi-continuous flow and continuous flow reactors; the operating temperature is 35-37℃, nitrogen blowing is carried out for 5-15min to realize the anaerobic environment in the reactor, and the reactor is placed in a constant temperature magnetic stirrer with a stirring rate of 100-150r / min.

[0027] Compared with the prior art, the present application has the following beneficial effects:

[0028] (1) The present application prepares a tannic acid modified iron-biochar composite conductive carrier by a simple low-temperature hydrothermal synthesis method, which has low raw material cost, simple method, good conductivity, recyclability and high stability.

[0029] (2) The tannic acid modified iron-biochar novel conductive carrier prepared by the present application can store and release electrons, enhance the direct interspecies electron transfer between acid-producing bacteria and methanogenic bacteria in the anaerobic treatment process, and the carbon felt immobilization is conducive to the formation of biofilm, which not only solves the problem of recycling of conductive materials, but also significantly improves the methane production. BRIEF DESCRIPTION OF DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of the provided drawings.

[0031] Figure 1Preparation flow chart of iron-biochar, tannic acid modified iron-biochar composite conductive material / carriers in Example 1.

[0032] Figure 2 Scanning electron microscope images of iron-biochar, tannic acid modified iron-biochar composite conductive material (a) and carriers (b) in Example 1.

[0033] Figure 3 Cyclic voltammogram (a) and electrochemical impedance (b) of iron-biochar, tannic acid modified iron-biochar composite conductive carrier material in Example 2.

[0034] Figure 4 Structural schematic diagram of anaerobic biological reaction processor in Example 3 and 4.

[0035] Figure 5 TOC concentration change (a) and total biogas production (b) of iron-biochar, tannic acid modified iron-biochar composite conductive carrier material in Example 3 in the process of enhanced wastewater anaerobic biological treatment at different reaction times.

[0036] Figure 6 TOC concentration change (a) and total biogas production (b) of iron-biochar, tannic acid modified iron-biochar composite conductive carrier material in Example 4 in the process of enhanced wastewater anaerobic biological treatment at different reaction times. DETAILED DESCRIPTION

[0037] The technical solutions in the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0038] Herein, the special word "embodiment" as "exemplary" of any embodiment does not necessarily explain as superior or better than other embodiments. The performance index test in the embodiments of the present application adopts the conventional test method in the art, unless otherwise specified. It should be understood that the terms described in the present application are only for describing the specific embodiments, and are not used to limit the disclosure of the present application.

[0039] Unless otherwise specified, the technical and scientific terms used herein have the same meanings as generally understood by those skilled in the art to which the present application belongs; as the test methods and technical means not specially noted in the present application refer to the experimental methods and technical means generally used by those skilled in the art.

[0040] For a better understanding of the present application, numerous specific details are given in the following detailed description. The person skilled in the art understands that the present application can also be implemented without certain specific details. In the examples, some methods, means, instruments, devices, etc. that are well known to the person skilled in the art are not described in detail in order to highlight the gist of the present application.

[0041] The technical features disclosed in the embodiments of the present application can be combined arbitrarily without conflict, and the resulting technical solutions belong to the disclosure of the present application.

[0042] The application discloses a tannic acid modified iron-biochar composite conductive carrier material and a preparation method and application thereof.

[0043] For a better understanding of the present application, the following examples are further described in detail, but it should not be understood as limiting the present application. Some non-essential improvements and adjustments made by the person skilled in the art according to the above content are also regarded as falling within the scope of protection of the present application.

[0044] Example 1

[0045] A preparation method of a tannic acid modified iron-biochar composite conductive carrier material comprises the following steps:

[0046] (1) wood raw material is calcined at high temperature to obtain biochar, and after natural cooling, the biochar is washed alternately with deionized water and ethanol, dried, and sieved for use;

[0047] (2) the biochar and FeCl3·6H2O are dissolved in deionized water and magnetically stirred for 30 min;

[0048] (3) after sufficient dissolution, tannic acid (TA) is added and stirring is continued for 6 h, and the pH value of the obtained mixed solution is adjusted to 7 by NaOH;

[0049] (4) the mixed solution in step (3) is transferred into a 100 mL reaction kettle together with pretreated carbon felt for hydrothermal synthesis, and after natural cooling, the mixture is washed with deionized water and vacuum dried to obtain a tannic acid modified iron-biochar composite conductive carrier material, which is named Fe-TA-C@CF.

[0050] In step (1), the biochar is wood biochar, the calcination temperature is 500 DEG C, the calcination time is 2 h, the biochar is washed alternately with deionized water and ethanol for 3 times, dried at 60 DEG C, the drying time is 12 h, and the sieved 150 mesh powder is used.

[0051] In step (2), 1.0 g of biochar and 0.02 g of FeCl3·6H2O are sequentially added into 40 mL of deionized water.

[0052] In step (3), 0.06 g of tannic acid was added, the molar ratio of tannic acid to iron was 1:2, and 0.1 M NaOH solution was added dropwise until the pH of the mixed solution was 7.

[0053] In step (4), the pretreatment method of the carbon felt was as follows: the 2x2x0.2 cm carbon felt was soaked in a 30% mass concentration hydrogen peroxide solution at 90°C in a water bath for 1.5 h. After washing with deionized water to neutral pH, drying in an oven at 60°C for 5 h, the pretreated carbon felt was obtained. 3

[0054] In step (4), the hydrothermal temperature was 120°C, the hydrothermal synthesis time was 14 h, the vacuum drying temperature was 60°C, and the drying time was 12 h.

[0055] In step (3), no TA was added, and the other steps were the same, to prepare an iron-biochar composite conductive carrier material, named Fe-C@CF; in step (4), no carbon felt was added, and the other steps were the same, to prepare an iron-biochar composite material, named Fe-TA-C; in step (3), no TA was added, and in step (4), no carbon felt was added, and the other steps were the same, to prepare a tannic acid modified iron-biochar composite material, named Fe-C.

[0056] The preparation flow chart is shown in Figure 1 The scanning electron microscope images of the composite materials Fe-TA-C (a) and carrier Fe-TA-C@CF (b) prepared by the above method are shown in Figure 2 .

[0057] Example 2

[0058] A method for preparing a tannic acid modified iron-biochar composite conductive carrier material, comprising the following steps:

[0059] (1) wood raw material was calcined at high temperature to obtain biochar, which was washed with deionized water and ethanol alternately after natural cooling, dried, and sieved;

[0060] (2) the biochar and FeCl3·6H2O were dissolved in deionized water and magnetically stirred for 40 min;

[0061] (3) after complete dissolution, tannic acid (TA) was added and stirring was continued for 8 h, and the pH of the obtained mixed solution was adjusted to 9 using NaOH;

[0062] (4) the mixed solution in step (3) was transferred into a 100 mL reaction kettle together with pretreated carbon felt to perform hydrothermal synthesis, washed with deionized water after natural cooling, and vacuum dried to obtain a tannic acid modified iron-biochar composite conductive carrier material, named Fe-TA-C@CF. ​

[0063] In step (1), the biochar is wood biochar, the calcination temperature is 550℃, the calcination time is 1.5h, the biochar is washed with deionized water and ethanol alternately for 3 times, and is dried at 60℃ for 12h, and then is sieved to obtain 100 mesh powder for use.

[0064] In step (2), 1.0g of biochar and 0.05g of FeCl3·6H2O are sequentially added into 50mL of deionized water.

[0065] In step (3), 0.31g of tannic acid is added, the molar ratio of tannic acid to iron is 1:1, and 0.2M NaOH solution is added dropwise until the pH of the mixed solution is 9.

[0066] In step (4), the pretreatment method of the carbon felt is as follows: the carbon felt with the size of 4×4×0.1cm 3 is soaked in 30% hydrogen peroxide solution at 85℃ water bath for 2h. The carbon felt is washed with deionized water until the pH value is neutral, and is dried in an oven at 60℃ for 6h to obtain the pretreated carbon felt.

[0067] In step (4), the hydrothermal temperature is 130℃, the hydrothermal synthesis time is 16h, the carbon felt is washed with deionized water for 3 times after being naturally cooled to below 60℃, the vacuum drying temperature is 65℃, and the drying time is 8h.

[0068] In step (3), no TA is added, and the other steps are the same, to obtain an iron-biochar composite conductive carrier material, which is named Fe-C@CF.

[0069] The composite conductive carrier materials Fe-C@CF and Fe-TA-C@CF prepared by the above method are subjected to electrochemical cyclic voltammetry curve CV (a) and electrochemical impedance spectrum EIS (b) tests, and the data are shown in Figure 3 At a scan rate of 50mV / s, the electrochemical active area (ECSA) of Fe-TA-C@CF is higher than that of Fe-C@CF, which is calculated by integrating the CV curve (a). The electronic transfer resistance (Rct) of the EIS spectrum (b) is calculated by equivalent circuit, and it is found that Fe-TA-C@CF<Fe-C@CF.

[0070] Therefore, it is illustrated that the interface mass transfer resistance can be significantly reduced due to the doping of the appropriate Fe-TA molar ratio; compared with Fe-C@CF, Fe-TA-C@CF has more active sites, stronger conductivity and smaller electron transfer resistance, which can create a more suitable growth environment for anaerobic microorganisms, and finally enhance the direct interspecies electron transfer DIET.

[0071] Example 3

[0072] A preparation method of a tannic acid modified iron-biochar composite conductive carrier material, comprising the following steps:

[0073] (1) Wood raw material is calcined at high temperature to obtain biochar, which is washed alternately with deionized water and ethanol after natural cooling, dried, and sieved for use;

[0074] (2) The biochar and FeCl3·6H2O are dissolved in deionized water and magnetically stirred for 30 min;

[0075] (3) After sufficient dissolution, tannic acid (TA) is added and stirring is continued for 6 h, and the pH value of the obtained mixed solution is adjusted to 8 by using NaOH;

[0076] (4) The mixed solution in step (3) is transferred into a 100 mL reaction kettle together with pretreated carbon felt to perform hydrothermal synthesis, washed with deionized water after natural cooling, vacuum dried, to obtain a tannic acid modified iron-biochar composite conductive carrier material, named Fe-TA-C@CF.

[0077] In step (1), the biochar is wood biochar, the calcination temperature is 450℃, the calcination time is 3h, the deionized water and ethanol are alternately washed 4 times, dried at 65℃, the drying time is 8h, and the sieved 150 mesh powder is used.

[0078] In step (2), 1.0g of biochar and 0.02g of FeCl3·6H2O are sequentially added into 40mL of deionized water.

[0079] In step (3), 0.04g of tannic acid is added, the molar ratio of tannic acid to iron is 1:3, and 0.1M NaOH solution is added dropwise until the pH of the mixed solution is 8.

[0080] In step (4), the pretreatment method of the carbon felt is that the carbon felt with a size of 5×5×0.1cm 3 is soaked in a 30% hydrogen peroxide solution at a water bath temperature of 90℃ for 1h. After being washed with deionized water to neutral pH and dried in a 65℃ oven for 3h, the pretreated carbon felt is obtained.

[0081] In step (4), the hydrothermal temperature is 140℃, the hydrothermal synthesis time is 12h, the mixed solution is washed with deionized water for 3 times after natural cooling to below 60℃, and the vacuum drying temperature is 65℃, and the drying time is 8h.

[0082] Wherein, in step (3), TA is not added, and other steps are consistent, to prepare a iron-biochar composite conductive carrier material, named Fe-C@CF; in step (4), carbon felt is not added, and other steps are consistent, to prepare a iron-biochar composite material, named Fe-TA-C; in step (3), TA is not added, and in step (4), carbon felt is not added, and other steps are consistent, to prepare a tannic acid modified iron-biochar composite material, named Fe-C.

[0083] In order to further prove the beneficial effects of the present application and better understand the present application, the technical features disclosed in the present application are further illustrated by the following application examples, but can not be understood as limiting the present application. Other improvements without creative work made by those skilled in the art according to the above invention content are also regarded as falling within the protection scope of the present application.

[0084] Application Example 1

[0085] An application of a tannic acid modified iron-biochar composite conductive carrier material, specifically:

[0086] Anaerobic sludge and Fe-C / Fe-TA-C prepared by the method of Example 3 were placed in a 250 mL anaerobic reaction bottle, 200 mL of simulated municipal wastewater was introduced, and mixed culture was carried out for 10 days to biodegrade organic pollutants, pH was maintained at 8.0, and hydraulic retention time was 12 h. The anaerobic sludge was taken from an anaerobic UASB reactor which had been stably operated for 1 year in the laboratory, the sludge concentration was 6 gVSS / L, and the addition amount of Fe-C / Fe-TA-C was 0.05 g / L. The liquid zone at the bottom of the reaction bottle was the main reaction zone, and the upper part was the headspace gas, which was connected to a gas collection bag for collecting biogas produced by the reactor. The sampling port was sealed with a water stop clamp at the bottom of the hose. Nitrogen was introduced for 10 min to ensure the anaerobic environment. After the anaerobic reaction bottle was connected, it was placed in a constant temperature magnetic stirrer at 35℃ and cultured at a speed of 100 r / min. The COD concentration of the simulated municipal wastewater was 500 mg COD / L (sodium acetate: glucose = 1:1), and ammonium chloride and potassium dihydrogen phosphate were used to provide nitrogen and phosphorus sources required for microbial growth and metabolism, respectively, wherein the mass ratio of carbon, nitrogen and phosphorus was 100:5:1, and the concentration of sodium bicarbonate was 500 mg / L. After 20 cycles, the TOC in the solution was measured at 4 h, 8 h, 12 h of the 1st, 3rd, 5th, 7th, 9th, 11th, 13th, 15th, 17th, 19th cycle, and the cumulative gas production and components were measured at the end of the 20th cycle to evaluate the strengthening effect of the Fe-C / Fe-TA-C conductive composite material on anaerobic digestion of municipal wastewater.

[0087] As Figure 5(a) shows the change of TOC with time tested by total organic carbon analyzer to explore the removal rate of organic matter, and the control group is the anaerobic bioreactor without conductive material, named control. As can be seen from the figure, the TOC degradation rate is fast first and then slow, and the removal rate of TOC in the conductive material group is higher than that in the control group. Compared with the control group (75-80%), the TOC removal rate under the dosage of 0.05 g / L Fe-C increased to 88-90%. The addition of Fe-TA-C with the same concentration, the TOC removal rate is 95-97%, increased by about 25%.

[0088] Figure 5 (b) in the control group, Fe-C, Fe-TA-C group, the cumulative gas production in the whole reaction process collected with gas bag is detected by gas chromatography (TCD), the main components are methane (CH4) and CO2. Compared with the control group, the cumulative methane production of Fe-C, Fe-TA-C group increased by 0.49, 1.03 times respectively, and the performance of Fe-TA-C is better than that of Fe-C. It is proved that the simple low-temperature hydrothermal synthesis of tannic acid modified iron-biochar composite conductive carrier material can be used as an excellent electron transfer carrier, promote the direct interspecies electron transfer between hydrolytic acidification bacteria and methanogenic bacteria, and improve the removal rate of organic matter and methane production.

[0089] Application example 2

[0090] The application of a tannic acid modified iron-biochar composite conductive carrier material, specifically:

[0091] Anaerobic sludge and Fe-C@CF / Fe-TA-C@CF prepared by the method of example 4 were placed in a 250 mL anaerobic reaction bottle, 200 mL of simulated municipal wastewater was introduced, and mixed culture was carried out for 10 days to biodegrade organic pollutants, the pH was maintained at 7.5, and the hydraulic retention time was 12 h. The anaerobic sludge was taken from the laboratory stable operation for 1 year anaerobic UASB reactor, the sludge concentration was 5 gVSS / L, and a piece of Fe-C@CF / Fe-TA-C@CF carrier with effective contact area of 2×2×0.1 cm 3, the load is 0.01 g, which is equivalent to the dosage of 0.05 g / L, the liquid zone at the bottom of the reaction bottle is the main reaction zone, the upper part is the headspace gas, the gas bag is connected with it for collecting the biogas produced by the reactor, and the carrier is fixed suspended in the reaction bottle. The sampling port is sealed with a water stop clamp at the bottom of the hose. Nitrogen is exposed for 15 min to ensure anaerobic environment. After connecting the anaerobic reaction bottle, it is placed in a constant temperature magnetic stirrer at 37℃, and the rotation speed is kept at 150 r / min. The COD concentration of the simulated municipal wastewater is 500 mg COD / L (sodium acetate: glucose = 1:1), and ammonium chloride and potassium dihydrogen phosphate are used to provide nitrogen and phosphorus sources required for microbial growth and metabolism, respectively. The mass ratio of carbon, nitrogen and phosphorus is 100:5:1, and the concentration of sodium bicarbonate is 500 mg / L as a pH buffer. Cycle 20 times, take water samples at 4h, 8h, 12h of 1st, 3rd, 5th, 7th, 9th, 11th, 13th, 15th, 17th, 19th cycle to measure TOC in solution, and measure cumulative gas production and components at the end of 20 cycles to evaluate the effect of Fe-C@CF / Fe-TA-C@CF composite conductive carrier material on the synergistic regulation of microbial-carrier interface in anaerobic biological treatment of municipal wastewater.

[0092] As shown in Figure 6 (a), the change of TOC with time was tested by total organic carbon analyzer to explore the removal rate of organic matter, and the control group was the anaerobic bioreactor without adding conductive carrier, named control. As can be seen from the figure, the TOC degradation rate is fast first and then slow, and the TOC removal rate in the conductive carrier group is higher than that in the control group. Compared with the control group (75-80%), the TOC removal rates of the reactors introducing Fe-C@CF and Fe-TA-C@CF are 90-92% and 94-95%, respectively.

[0093] Figure 6 (b), the cumulative gas production in control, Fe-C@CF and Fe-TA-C@CF groups during the whole reaction process was collected by gas bag and detected by gas chromatography (TCD). Compared with the control group, the cumulative methane production of Fe-C and Fe-TA-C groups increased by 1.76 and 1.85 times, respectively. It shows that tannic acid modified iron-biochar composite conductive carrier material can store and release electrons, induce the formation of functional biofilm, strengthen the electron transfer between microorganisms and carrier interface, significantly improve the methane production, solve the problem of recovery of conductive materials, and has low raw material cost and high stability. It has technical, environmental and economic advantages, and is expected to become a sustainable alternative to traditional carriers in anaerobic wastewater biological treatment system.

[0094] The foregoing description of the disclosed embodiments enables a person skilled in the art to make or use the application. Modifications of these embodiments will occur to persons of skill in the art, and that the appended claims are intended to cover all such modifications that do not depart from the true spirit and scope of the application. Therefore, the application is not limited to the embodiments shown but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a tannic acid-modified iron-biochar composite conductive carrier material, characterized in that, The method specifically includes the following steps: (1) The wood raw material was calcined at high temperature to obtain biochar. After natural cooling, it was washed alternately with deionized water and ethanol, dried and sieved for later use. (2) Dissolve the biochar and soluble iron salt obtained in step (1) in deionized water and stir magnetically. (3) After the solution is fully dissolved, add tannic acid (TA) and adjust the pH of the resulting mixed solution with alkali solution; (4) The mixed solution in step (3) and the pretreated carbon felt are transferred to the reactor for hydrothermal synthesis. After natural cooling, the mixture is washed with deionized water and vacuum dried to obtain the tannic acid modified iron-biochar composite conductive carrier material.

2. The preparation method of the tannic acid-modified iron-biochar composite conductive carrier material according to claim 1, characterized in that, In step (1), the biochar is wood-based biochar; the calcination temperature is 450-550℃, the calcination time is 1-3h, and the heating rate is 5-10℃ / min; it is washed 3-4 times alternately with deionized water and ethanol, dried at 60-65℃ for 8-12h, and sieved to obtain 100-150 mesh powder for later use.

3. The preparation method of the tannic acid-modified iron-biochar composite conductive carrier material according to claim 1, characterized in that, In step (2), add 0.50-1.0g of biochar and 0.02-0.05g of soluble iron salt to every 40-50mL of deionized water.

4. The preparation method of the tannic acid-modified iron-biochar composite conductive carrier material according to claim 1, characterized in that, In step (3), add 0.04-0.32g of tannic acid, with a molar ratio of tannic acid to iron of 1:1-1:

3. Add the tannic acid dropwise with 0.1-0.2M NaOH or KOH solution until the pH of the mixed solution is 7-9.

5. The preparation method of the tannic acid-modified iron-biochar composite conductive carrier material according to claim 1, characterized in that, In step (4), the carbon felt pretreatment method is as follows: under a water bath at 80-90℃, 2-5×2-5×0.1-0.2cm 3 The carbon felt was soaked in a 30% hydrogen peroxide solution for 1-2 hours; rinsed with deionized water until the pH value was neutral; and dried in an oven at 60-65℃ for 3-6 hours to obtain the pretreated carbon felt.

6. The method for preparing the tannic acid-modified iron-biochar composite conductive carrier material according to claim 1 or 5, characterized in that, In step (4), the hydrothermal temperature is 120-140℃, the hydrothermal synthesis time is 12-16h, after natural cooling to below 60℃, it is washed with deionized water 3-4 times, the vacuum drying temperature is 60-65℃, and the drying time is 8-12h.

7. A tannic acid-modified iron-biochar composite conductive carrier material prepared by the method described in claim 1, characterized in that, The conductive carrier material is a Fe-TA-C composite conductive carrier material that promotes electron transfer.

8. The application of a tannic acid-modified iron-biochar composite conductive carrier material prepared by the method described in claim 1 in environmental remediation and pollution control technologies.

9. The application according to claim 8, characterized in that, The application of the tannic acid-modified iron-biochar composite conductive carrier material in anaerobic treatment of wastewater.

Images