A method for treating low-cod concentration wastewater

Abstract

The application discloses a low COD concentration wastewater treatment method, which is carried out in an anaerobic membrane bioreactor (AnMBR) which comprises a reactor body, the lower part of the reactor body is filled with anaerobic granular sludge loaded with conductive material, cathode and anode electrode sheets are inserted between the anaerobic granular sludge, the cathode and anode electrode sheets are opposite to each other in pairs to form a group, the electrode sheets are electrically connected with a power supply device arranged outside the reactor body, and the cathode electrode sheets are arranged in a filtering cavity formed by hollow fiber membranes and the like. The equipment used in the method has simple structure, the method is easy to operate, and the universality is extremely high.

Description

Technical Field

[0001] This invention relates to the field of anaerobic methanogenesis technology, and in particular to a method for treating wastewater with low COD concentration. Background Technology

[0002] The basic principle of anaerobic methanogenesis in wastewater treatment is to utilize anaerobic and facultative anaerobic microbial communities to gradually decompose complex organic substrates in wastewater into methane and carbon dioxide; this process is also known as anaerobic digestion. The methanogenic capacity during anaerobic digestion largely depends on interspecies electron transfer. Direct interspecies electron transfer (DIET) uses conductive pili, cytochrome c, and conductive materials to transfer electrons from bacteria to methanogenic archaea. DIET provides a more efficient way to promote methanogenesis without requiring additional energy to produce H2 as an electron shuttle.

[0003] Anaerobic granular sludge (AGS) is considered a microbial aggregate composed of microorganisms and extracellular polymeric substances (EPS). Compared to suspended sludge, it exhibits superior settling ability and high metabolic activity. Acid-producing bacteria and methanogens are the two main symbiotic groups in AGS. Acid-producing bacteria are mainly distributed in the outer layer of AGS, capable of converting organic compounds into small-molecule acids and H2 / CO2 while generating electrons. Methanogens are mainly distributed in the inner layer of AGS, utilizing the products and electrons generated during fermentation to biosynthesize methane. Therefore, the methanogenic capacity of AGS largely depends on interspecies electron transfer between acid-producing and methanogens. However, the EPS in AGS contains a large amount of non-conductive material, limiting the DIET process. Loading conductive materials inside AGS or applying an external electric field can promote methanogenesis in AGS.

[0004] Conductive materials can alter microbial communities, promote the enrichment of functional microorganisms, and accelerate the consumption of VFAs, thereby increasing CH4 production. From an economic perspective, they should be widely available and have readily available raw materials; from the perspective of their effect on methanogenic systems, they should possess the characteristics of material stability and resistance to decomposition. Commonly used iron-based media for promoting the DIET process in anaerobic biological wastewater treatment include Fe3O4, Fe2O3, nZVI, and stainless steel; carbon-based materials include AC, CNT, and carbon cloth. Anaerobic membrane bioreactors (AnMBRs) combine membrane separation units and AD (anaerobic digestion) to avoid the loss of sludge and materials during anaerobic digestion. During AnMBR operation, membrane fouling is mainly caused by EPS (extracellular polymeric substances). By controlling the dense structure of EPS with an electric field, the non-conductive components in EPS are oxidized and decomposed, reducing charge transfer resistance, increasing methane production, and enhancing COD removal rate.

[0005] Therefore, regulating the composition and electrochemical activity of EPS is crucial for improving methane production and controlling membrane fouling in anaerobic membrane bioreactors. An improved anaerobic reactor is urgently needed to address these issues. Summary of the Invention

[0006] The purpose of this invention is to address the technical deficiencies in the existing technology by providing a method for treating wastewater with low COD concentration.

[0007] The technical solution adopted to achieve the purpose of this invention is:

[0008] A method for treating low COD wastewater is disclosed, which is carried out in an anaerobic membrane bioreactor (AnMBR). The anaerobic membrane bioreactor includes a reactor body, the lower part of which is filled with anaerobic granular sludge loaded with conductive material. The surface channels of the anaerobic granular sludge are opened by a structure regulator. Cathode and anode electrode plates are inserted between the anaerobic granular sludge particles, and the cathode and anode electrode plates are arranged in pairs facing each other. The electrode plates are electrically connected to a power supply device located outside the reactor body. The cathode electrode plate is located in a filter chamber formed by a hollow fiber membrane. The filter chamber is connected to an effluent pipe, and an effluent pump is installed on the effluent pipe. The electrode plates are used to adjust the dense structure of extracellular polymers in the anaerobic granular sludge, so that the extracellular polymers are oxidized and decomposed, thereby increasing the methanogenic output and mitigating the fouling of the hollow fiber membrane by the low COD wastewater.

[0009] The reactor body is equipped with a water distribution plate located below the anaerobic granular sludge. Multiple water distribution ports are provided on the water distribution plate. The water distribution plate is connected to an inlet pipe connected to an inlet pump. The inlet pump pumps low COD concentration wastewater into the reactor body through the water distribution plate, so that it can fully contact the anaerobic granular sludge.

[0010] The reactor body is fixed with an orifice plate and a three-phase separator. The orifice plate is located above the anaerobic granular sludge, and the three-phase separator is located above the orifice plate. The three-phase separator separates the anaerobic granular sludge and methane. An exhaust pipe is provided on the reactor body above the three-phase separator. The exhaust pipe is connected to a gas collection bag through a negative pressure air pump device to collect methane.

[0011] The processing method includes the following steps:

[0012] At 20-25℃, low COD concentration wastewater is pumped into the reactor body through an influent pump, where it comes into full contact with anaerobic granular sludge. The anaerobic granular sludge utilizes the low COD concentration wastewater to produce methane, which is simultaneously pumped into a gas collection bag through a negative pressure air extraction pump. After 1-2 days, the purified water is discharged through a drain pipe. During this process, the hollow fiber membrane fouling is monitored by monitoring changes in transmembrane pressure (TMP). When TMP reaches 80 kPa, the hollow fiber membrane is physically and chemically cleaned or replaced with a new membrane.

[0013] In the above technical solution, the anode electrode sheet is made of graphite plate, and a DC power supply of 1V is applied to the cathode electrode sheet and the anode electrode sheet.

[0014] In the above technical solution, the cathode electrode sheet is made of stainless steel mesh, and the hollow fiber membrane is a PVDF hollow fiber membrane, a PTFE hollow fiber membrane, or a carbon nanotube hollow fiber membrane.

[0015] In the above technical solution, the anaerobic granular sludge loaded with conductive material is prepared through the following steps:

[0016] Anaerobic granular sludge is acclimated until the effluent COD concentration stabilizes. The supernatant is then discharged, and a dispersion consisting of a structure regulator and simulated low-COD wastewater is added. The pH is adjusted to 7 to open the pores on the surface of the anaerobic granular sludge for structure regulation. The supernatant is then discharged, and a suspension formed in simulated low-COD wastewater using carbon-based or iron-based conductive materials is added. After the anaerobic granular sludge and suspension have been in full contact, the supernatant is discharged, yielding anaerobic granular sludge loaded with conductive materials.

[0017] In the above technical solution, under anaerobic conditions, simulated low COD concentration wastewater is added to the anaerobic granular sludge to acclimate the anaerobic granular sludge; during acclimatization, the simulated low COD concentration wastewater is replaced every two days as a cycle, and the acclimatization time is 10-20 days.

[0018] In the above technical solution, the structure regulator is one or more of (Z-)-4-bromo-5-(bromoethylene)-2(5H)-furanone (BBF), vanillin, alkyl glycoside (APG), bis(3-aminopropyl)amine, and D-type amino acids. Each liter of the dispersion contains 1-20 mg of BBF, 1-200 mg of vanillin, 1-5 g of alkyl glycoside (APG), 0.5-1 g of D-type amino acids, and 100-500 μL of bis(3-aminopropyl)amine.

[0019] In the above technical solution, each liter of simulated low COD concentration wastewater contains 0.255–0.6375 g of anhydrous sodium acetate (COD content of 500 mg), 0.4 g of NH4Cl, 1 g of NaHCO3, 0.4 g of MgSO4·7H2O, 0.4 g of KCl, 0.5 g of CaCl2·2H2O, 0.08 g of (NH4)2HPO4, 5 mL of vitamin solution, and 12.5 mL of trace element solution.

[0020] In the above technical solution, the carbon-based conductive material is one or more of powdered activated carbon (PAC), carbon black (CB), multi-walled carbon nanotubes (MWCNT), carbon cloth, and biochar, and the suspension contains 50-200 mg of carbon-based conductive material per liter.

[0021] In the above technical solution, the iron-based conductive material is one or a mixture of Fe3O4NPs, Fe2O3NPs, nZVI or stainless steel, and the suspension contains 50 to 500 mg of the iron-based conductive material, and the particle size of the iron-based conductive material is 20 to 50 nm.

[0022] Compared with the prior art, the beneficial effects of the present invention are:

[0023] 1. Extracellular polymers within anaerobic granular sludge not only foul hollow fiber membranes but also restrict interspecies electron transfer within the anaerobic granular sludge. This invention modulates the composition and electrochemical activity of extracellular polymers by placing electrode plates between anaerobic granular sludge particles, thereby oxidizing and decomposing them, which is crucial for improving methane production in anaerobic membrane bioreactors and controlling membrane fouling.

[0024] 2. The anaerobic granular sludge of this invention is loaded with iron-based and carbon-based conductive materials. The iron-based conductive materials can form electron transport channels between symbiotic microorganisms and simultaneously stimulate the secretion of cytochrome c. The carbon-based conductive materials provide a larger reaction surface area for microorganisms, which is beneficial for their attachment. They can also adsorb toxic compounds using their large pore size to avoid interfering with the methanogenesis process. Therefore, this invention promotes direct electron transport, reduces charge transport resistance, and significantly increases methane production. Attached Figure Description

[0025] Figure 1 This is a comparison chart of the effluent tCOD concentrations of anaerobic granular sludge from Example 1, anaerobic granular sludge from Comparative Example 1, and ordinary anaerobic granular sludge.

[0026] Figure 2 This is a comparison chart of the effluent tCOD concentrations of the anaerobic granular sludge from Example 2, the anaerobic granular sludge from Comparative Example 2, and ordinary anaerobic granular sludge.

[0027] Figure 3 This is a comparison chart of the effluent tCOD concentrations of the anaerobic granular sludge from Example 3, the anaerobic granular sludge from Comparative Example 3, and ordinary anaerobic granular sludge.

[0028] Figure 4 This is a comparison chart of the effluent tCOD concentrations of the anaerobic granular sludge from Example 4, the anaerobic granular sludge from Comparative Example 4, and ordinary anaerobic granular sludge.

[0029] Figure 5This is a comparison chart of the effluent tCOD concentrations of the anaerobic granular sludge from Example 5, the anaerobic granular sludge from Comparative Example 5, and ordinary anaerobic granular sludge.

[0030] Figure 6 This is a comparison chart of the effluent tCOD concentrations of the anaerobic granular sludge from Example 6, the anaerobic granular sludge from Comparative Example 6, and ordinary anaerobic granular sludge.

[0031] Figure 7 This is an overall cross-sectional view of the anaerobic membrane bioreactor.

[0032] Figure 8 This is a partially enlarged view of the anaerobic membrane bioreactor.

[0033] Among them, 1: anaerobic granular sludge, 2: electrode plate, 3: power supply device, 4: water distribution plate, 5: water distribution port, 6: water inlet pipe, 7: water inlet pump, 8: orifice plate, 9: three-phase separator, 10: water outlet pipe, 11: air outlet pipe, 12: air collection bag, 13: negative pressure air pump device, 14: hollow fiber membrane, 15: water outlet pump. Detailed Implementation

[0034] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention.

[0035] The anaerobic granular sludge (raw material) came from the anaerobic tower of a citric acid manufacturer in Shandong Province.

[0036] Example 1

[0037] like Figures 7-8 As shown, a method for treating low COD wastewater is carried out in an anaerobic membrane bioreactor (AnMBR). The anaerobic membrane bioreactor includes a reactor body, the lower part of which is filled with anaerobic granular sludge 1 loaded with conductive material. The surface channels of the anaerobic granular sludge 1 are opened by a structure regulator. Cathode and anode electrode plates 2 are inserted between the anaerobic granular sludge 1, and the cathode and anode electrode plates 2 are paired together. The electrode plates 2 are electrically connected to a power supply device 3 located outside the reactor body. The cathode electrode plate is located in a filter chamber formed by a hollow fiber membrane 14. The filter chamber is connected to an effluent pipe 10. An effluent pump 15 is installed on the effluent pipe 10. The electrode plates 2 are used to adjust the dense structure of the extracellular polymers in the anaerobic granular sludge 1, so that the extracellular polymers are oxidized and decomposed, increasing the methanogenic output and mitigating the fouling of the hollow fiber membrane by the low COD wastewater.

[0038] The reactor body is provided with a water distribution plate 4, which is located below the anaerobic granular sludge 1. Multiple water distribution ports 5 are opened on the water distribution plate 4. The water distribution plate 4 is connected to the water inlet pipe 6 connected to the water inlet pump 7. The water inlet pump 7 pumps low COD concentration wastewater into the reactor body through the water distribution plate 4, so that it can fully contact the anaerobic granular sludge 1.

[0039] The reactor body is fixed with an orifice plate 8 and a three-phase separator 9. The orifice plate 8 is located above the anaerobic granular sludge 1, and the three-phase separator 9 is located above the orifice plate 8. The three-phase separator 9 separates the anaerobic granular sludge 1 and methane. An exhaust pipe 11 is provided on the reactor body above the three-phase separator 9. The exhaust pipe 11 is connected to a gas collection bag 12 through a negative pressure air pump device 13 to collect methane.

[0040] The processing method includes the following steps:

[0041] At 20-25℃, low COD concentration wastewater is pumped into the reactor body through inlet pump 7, and fully contacts the anaerobic granular sludge 1. The anaerobic granular sludge 1 uses the low COD concentration wastewater to produce methane, which is simultaneously pumped into the gas collection bag 12 through negative pressure air pump device 13. After 1-2 days, the purified water is discharged through the drain pipe. During this process, the hollow fiber membrane fouling is monitored by monitoring the change of transmembrane pressure (TMP). When TMP reaches 80kPa, the hollow fiber membrane is physically and chemically cleaned or replaced with a new membrane. The anode electrode plate 2 is made of graphite plate, and the cathode electrode plate is made of stainless steel mesh. A DC power supply of 1V is applied to the cathode electrode plate 2 and the anode electrode plate 2.

[0042] The method for preparing the anaerobic granular sludge loaded with conductive material includes the following steps:

[0043] In an anaerobic environment, anaerobic granular sludge (raw material) is cultured with simulated low-COD concentration wastewater to acclimate the sludge. During acclimatization, the simulated low-COD concentration wastewater is replaced every two days for 10-20 days. After the effluent COD concentration stabilizes, the supernatant is discharged, and a dispersion consisting of a structure regulator and simulated low-COD concentration wastewater is added to adjust the pH to 7. This opens the pores on the surface of the anaerobic granular sludge for structure regulation. The supernatant is then discharged, and a suspension formed by carbon-based or iron-based conductive materials in the simulated low-COD concentration wastewater is added. After the anaerobic granular sludge has sufficient contact with the suspension, the supernatant is discharged, yielding anaerobic granular sludge loaded with conductive materials. The supernatant contains a certain amount of carbon-based or iron-based conductive materials in the simulated low-COD concentration wastewater. The D-concentration wastewater contains 0.6375g of anhydrous sodium acetate (COD content of 500mg), 0.4g of NH4Cl, 1g of NaHCO3, 0.4g of MgSO4·7H2O, 0.4g of KCl, 0.5g of CaCl2·2H2O, 0.08g of (NH4)2HPO4, 5mL of vitamin solution, and 12.5mL of trace element solution. The structure regulator is a mixture of bis(3-aminopropyl)amine and D-type amino acids. In each liter of dispersion, the volume of bis(3-aminopropyl)amine is 450uL, and the mass of D-type amino acids is 0.6g. Each liter of the suspension contains 200mg of conductive material with a particle size of 20-50nm. The conductive material is Fe3O4NPs.

[0044] Comparative Example 1

[0045] Compared with Example 1, no structure modifier was added to this comparative example, but the remaining steps were the same as in Example 1.

[0046] Compared with the control group (raw material), the methane yield of Example 1 increased by 160% to 170%, and the methane yield of Comparative Example 1 increased by 90% to 100%.

[0047] like Figure 1 As shown, compared with ordinary anaerobic granular sludge, the effluent tCOD concentration of Example 1 decreased by 50% to 60%, and the effluent tCOD concentration of the comparative example decreased by 40% to 50%.

[0048] Example 2

[0049] The conductive material used in this embodiment is different from the conductive material in Example 1. The conductive material in this embodiment is Fe2O3NPs.

[0050] Comparative Example 2

[0051] Compared with Example 2, no structure modifier was added to this comparative example, but the remaining steps were the same as in Example 2.

[0052] Compared with ordinary anaerobic granular sludge, the methane production of Example 2 increased by 80% to 90%, and the methane production of Comparative Example 2 increased by 50% to 60%.

[0053] like Figure 2 As shown, compared with ordinary anaerobic granular sludge, the effluent tCOD concentration of Example 2 decreased by 20% to 30%, and the effluent tCOD concentration of Comparative Example 2 decreased by 10% to 20%.

[0054] Example 3

[0055] The conductive material used in this embodiment is different from the conductive material in Embodiment 1. The conductive material in this embodiment is nZVI.

[0056] Comparative Example 3

[0057] Compared with Example 3, no structure modifier was added to this comparative example, but the remaining steps were the same as in Example 3.

[0058] Compared with ordinary anaerobic granular sludge, the methane production of Example 3 increased by 130% to 140%, and the methane production of Comparative Example 3 increased by 60% to 70%.

[0059] like Figure 3 As shown, compared with ordinary anaerobic granular sludge, the effluent tCOD concentration of Example 3 decreased by 50% to 60%, and the effluent tCOD concentration of Comparative Example 3 decreased by 30% to 40%.

[0060] Example 4

[0061] The conductive material used in this embodiment is different from the conductive material in Embodiment 1. The conductive material used in this embodiment is PAC.

[0062] Comparative Example 4

[0063] Compared with Example 4, no structure modifier was added to this comparative example, but the remaining steps were the same as in Example 4.

[0064] Compared with ordinary anaerobic granular sludge, the methane production of Example 4 increased by 140% to 150%, and the methane production of Comparative Example 4 increased by 50% to 65%.

[0065] like Figure 4 As shown, compared with ordinary anaerobic granular sludge, the effluent tCOD concentration of Example 4 decreased by 80% to 90%, and the effluent tCOD concentration of Comparative Example 4 decreased by 40% to 50%.

[0066] Example 5

[0067] The conductive material used in this embodiment is different from the conductive material in Embodiment 1. The conductive material in this embodiment is CB.

[0068] Comparative Example 5

[0069] Compared with Example 5, no structure modifier was added to this comparative example, but the remaining steps were the same as in Example 5.

[0070] Compared with ordinary anaerobic granular sludge, the methane production of Example 5 was increased by 130% to 140%, and the methane production of Comparative Example 5 was increased by 40% to 50%.

[0071] like Figure 5 As shown, compared with ordinary anaerobic granular sludge, the effluent tCOD concentration of Example 5 decreased by 70% to 80%, and the effluent tCOD concentration of Comparative Example 5 decreased by 30% to 40%.

[0072] Example 6

[0073] The conductive material used in this embodiment is different from the conductive material in Embodiment 1. The conductive material used in this embodiment is MWCNT.

[0074] Comparative Example 6

[0075] Compared with Example 6, no structure modifier was added to this comparative example, but the remaining steps were the same as in Example 6.

[0076] Compared with ordinary anaerobic granular sludge, the methane production of Example 6 increased by 120% to 130%, and the methane production of Comparative Example 6 increased by 30% to 40%.

[0077] like Figure 6 As shown, compared with ordinary anaerobic granular sludge, the effluent tCOD concentration of Example 6 decreased by 60% to 70%, and the effluent tCOD concentration of Comparative Example 6 decreased by 40% to 50%.

[0078] The above description is only a preferred embodiment of the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for treating wastewater with low COD concentration, characterized in that, This method is carried out in an anaerobic membrane bioreactor, which includes a reactor body. The lower part of the reactor body is filled with anaerobic granular sludge loaded with conductive material. The surface channels of the anaerobic granular sludge are opened by a structure regulator. Cathode and anode electrode plates are inserted between the anaerobic granular sludge particles, and the cathode and anode electrode plates are arranged in pairs facing each other. The electrode plates are electrically connected to a power supply device located outside the reactor body. The cathode electrode plate is located in the filter chamber formed by the hollow fiber membrane. The filter chamber is connected to an effluent pipe. An effluent pump is installed on the effluent pipe. The electrode plates are used to adjust the dense structure of the extracellular polymers in the anaerobic granular sludge, so that the extracellular polymers are oxidized and decomposed, increasing the amount of methanogens produced and mitigating the pollution of the hollow fiber membrane by low COD concentration wastewater. The reactor body is equipped with a water distribution plate located below the anaerobic granular sludge. Multiple water distribution ports are provided on the water distribution plate. The water distribution plate is connected to an inlet pipe connected to an inlet pump. The inlet pump pumps low COD concentration wastewater into the reactor body through the water distribution plate, so that it can fully contact the anaerobic granular sludge. The reactor body is equipped with a perforated plate and a three-phase separator. The perforated plate is located above the anaerobic granular sludge, and the three-phase separator is located above the perforated plate. The three-phase separator separates the anaerobic granular sludge and methane. An exhaust pipe is installed on the reactor body above the three-phase separator. The exhaust pipe is connected to a gas collection bag via a negative pressure pump to collect methane. The structure regulator is one or more of BBF, vanillin, alkyl glycosides, bis(3-aminopropyl)amine, and D-type amino acids. The conductive material is a carbon-based conductive material or an iron-based conductive material. The carbon-based conductive material is one or more of powdered activated carbon, carbon black, multi-walled carbon nanotubes, carbon cloth, and biochar. The iron-based conductive material is one or more of Fe3O4NPs, Fe2O3NPs, nZVI, or stainless steel. The processing method includes the following steps: At 20-25℃, low COD concentration wastewater is pumped into the reactor body through an inlet pump. The low COD concentration wastewater comes into full contact with the anaerobic granular sludge. The anaerobic granular sludge uses the low COD concentration wastewater to produce methane, which is simultaneously pumped into a gas collection bag through a negative pressure air pump. After 1-2 days, the purified water is discharged through an outlet pipe. During this process, the hollow fiber membrane fouling is monitored by the change in TMP. When TMP reaches 80 kPa, the hollow fiber membrane is physically and chemically cleaned or replaced with a new membrane.

2. The processing method according to claim 1, characterized in that, The anode electrode is made of graphite plate, and a DC power supply of 1 V is applied to both the cathode and anode electrodes.

3. The processing method according to claim 1, characterized in that, The cathode electrode sheet is made of stainless steel mesh, and the hollow fiber membrane is a PVDF hollow fiber membrane, a PTFE hollow fiber membrane, or a carbon nanotube hollow fiber membrane.

4. The processing method according to claim 3, characterized in that, The anaerobic granular sludge loaded with conductive material is prepared through the following steps: In an anaerobic environment, anaerobic granular sludge is acclimated using simulated low-COD wastewater. After the effluent COD concentration stabilizes, the supernatant is discharged, and a dispersion consisting of a structure regulator and simulated low-COD wastewater is added. The pH is adjusted to 7 to open the pores on the surface of the anaerobic granular sludge for structure regulation. The supernatant is then discharged, and a suspension formed by carbon-based or iron-based conductive materials in the simulated low-COD wastewater is added. After the anaerobic granular sludge and the suspension have been in full contact, the supernatant is discharged, yielding anaerobic granular sludge loaded with conductive materials.

5. The processing method according to claim 4, characterized in that, During acclimatization, the simulated low COD concentration wastewater is replaced every two days as a cycle, and the acclimatization period is 10-20 days.

6. The processing method according to claim 5, characterized in that, Each liter of the dispersion contains 1–20 mg of BBF, 1–200 mg of vanillin, 1–5 g of alkyl glycoside, 0.5–1 g of D-amino acid, and 100–500 μL of bis(3-aminopropyl)amine.

7. The processing method according to claim 6, characterized in that, Each liter of simulated low COD concentration wastewater contains 0.255–0.6375 g of anhydrous sodium acetate, 0.4 g of NH4Cl, 1 g of NaHCO3, 0.4 g of MgSO4·7H2O, 0.4 g of KCl, 0.5 g of CaCl2·2H2O, 0.08 g of (NH4)2HPO4, 5 mL of vitamin solution, and 12.5 mL of trace element solution.

8. The processing method according to claim 7, characterized in that, The suspension contains 50 to 200 mg of the carbon-based conductive material per liter.

9. The processing method according to claim 7, characterized in that, The suspension contains 50 to 500 mg of the iron-based conductive material per liter, and the particle size of the iron-based conductive material is 20 to 50 nm.

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