Co-fermentation product and anaerobic fermentation method thereof

Abstract

The invention discloses a co-fermentation product and an anaerobic fermentation method thereof, and belongs to the field of sludge treatment. The co-fermentation product comprises residual sludge and auxiliary waste, the auxiliary waste comprises at least one of kitchen waste and agricultural waste; wherein the C / N value of the co-fermentation product is 20 / 1-30 / 1. The main purpose of the invention is to provide a co-fermentation product which is beneficial for promoting hydrolysis and acidification of excess sludge and generating more volatile fatty acids.

Description

Technical Field

[0001] The present invention relates to the technical field of sludge treatment, and more specifically, to a co-ferment and an anaerobic fermentation method thereof. Background Art

[0002] With the development of cities and the explosive growth of the economy, the output of surplus sludge in Chinese urban areas has increased significantly. Surplus sludge is the activated sludge discharged from the secondary sedimentation tank (or sedimentation area) in the activated sludge system and is a by-product of sewage treatment. Surplus sludge has high organic matter content, low calorific value and high water content, and has high utilization value. However, there is still much room for improvement in the current disposal methods of surplus sludge in terms of reduction, harmlessness and resource utilization. Anaerobic fermentation degrades the organic matter in sludge into CH4 and H2. However, due to the low added value of the products and the high carbon emission characteristics of this method, the existing technology currently pays more attention to fermenting organic matter into volatile fatty acids. The high added value of volatile fatty acids is not only greater than that of methane, but also greater than that of biohydrogen, and it will not cause secondary pollution. However, due to the poor biodegradability and low hydrolysis efficiency of surplus sludge, the efficiency of anaerobic fermentation to produce acid is greatly limited.

[0003] Co-fermentation, as an effective method to supplement the carbon source for anaerobic fermentation, has received more and more attention. It usually uses two or more substrates for simultaneous fermentation. The co-fermentation method can directly provide more carbon sources, adjust the pH, C / N value and more electron transfer substances of the fermented product, and at the same time has the advantages of diluting the concentration of toxic compounds in the system, reducing the volume of the reaction system and improving the buffer capacity of the system. Auxiliary waste generally has characteristics such as high biodegradability, inhomogeneity, low alkalinity and good electron transfer ability. Along with the mixing of auxiliary waste and surplus sludge, it can accelerate the hydrolysis and acidification stages of anaerobic fermentation of the microbial community. Under the action of electrochemical stimulation, the auxiliary waste transfers electrons to the extracellular polymer of the surplus sludge, promoting the hydrolysis and acidification of the surplus sludge.

[0004] Therefore, there is an urgent need for a co-ferment with better acid production effect and an anaerobic fermentation method. Summary of the Invention

[0005] 1. Technical Problems to be Solved by the Invention

[0006] The purpose of the present invention is to overcome the deficiency of poor acid production effect in anaerobic fermentation in the prior art, provide a co-ferment with better acid production effect, and provide an anaerobic fermentation method for the co-ferment.

[0007] 2. Technical Solutions

[0008] To achieve the above object, the technical solution provided by the present invention is as follows:

[0009] A co-ferment of the present invention comprises surplus sludge and auxiliary waste;

[0010] The auxiliary waste includes at least one of food waste and agricultural waste;

[0011] Among them, the C / N value of the co-ferment is 20 / 1 to 30 / 1.

[0012] Furthermore, the pH value of the co-ferment is 6.0 to 9.0.

[0013] Furthermore, the temperature of the co-ferment is 20.0 to 35.0 °C.

[0014] It should be noted that by adjusting the ratio of the auxiliary waste to the excess sludge, the C / N value of the co-ferment is 20 / 1 to 30 / 1, the pH value is 6 to 9, and the temperature is 20 to 35 °C, which is conducive to promoting the hydrolysis and acidification of the excess sludge and generating more volatile fatty acids; among them, the auxiliary waste mainly serves as an electron transfer medium to promote the hydrolysis and acidification process of the excess sludge, and secondly, it is used to mix with the excess sludge to achieve the conditions suitable for anaerobic fermentation to produce acid;

[0015] Specifically, the co-ferment ensures that anaerobic fermentation stops at the methane production stage and produces a high level of VFAs, which can effectively promote the conversion of excess sludge and auxiliary waste into volatile fatty acids, especially solving the problem that excess sludge is difficult to hydrolyze and acidify and has a low VFAs production.

[0016] On the other hand, most of the auxiliary waste is organic matter, and different toxic and harmful substances or precursor substances (such as nitrogen, sulfur, heavy metals, and oils) in it are mixed with the excess sludge to obtain the co-ferment, which can dilute the concentration or inhibit and reduce toxicity; the temperature of the co-ferment refers to the temperature that can be used after the fermentation materials are mixed.

[0017] Furthermore, the agricultural waste includes at least one of corn straw, wheat straw, rice straw, sorghum straw, cotton straw, rice husk, peanut shell, sunflower seed shell, cottonseed shell, sugarcane bagasse, pig manure, sugarcane leaf, tobacco leaf, and vegetable stem and leaf;

[0018] The food waste includes food scraps.

[0019] Furthermore, any excess sludge can be used.

[0020] Furthermore, the excess sludge can be the excess sludge in a sewage treatment plant for treating domestic sewage or the excess sludge in a sewage treatment plant for treating industrial wastewater.

[0021] The present invention also provides a preparation method of the above co-ferment, including:

[0022] Mix the remaining sludge and auxiliary waste to obtain the co-fermentate.

[0023] Further, the mixing can be carried out by stirring.

[0024] Further, the C / N value of the obtained co-fermentate is 20 / 1 to 30 / 1, the pH value is 6 to 9, and the temperature is 20 to 35 °C.

[0025] Further, before mixing, the auxiliary waste also includes crushing.

[0026] Further, the conditions for the crushing include: making the particle size of the auxiliary waste 1 to 5 mm.

[0027] It should be noted that the auxiliary waste is crushed, and the particle size after crushing can be within the range of 1 to 5 mm.

[0028] The present invention also provides an anaerobic fermentation method using the above co-fermentate.

[0029] Carry out anaerobic fermentation of the co-fermentate in a fermentation tank.

[0030] Further, the anaerobic fermentation method of the co-fermentate includes the following steps:

[0031] S1. Feed the co-fermentate into the fermentation tank;

[0032] S2. Blow off the inside of the fermentation tank with an inert gas;

[0033] S3. Carry out anaerobic fermentation in the fermentation tank;

[0034] S4. Collect the treated sludge, supernatant and gas.

[0035] Further, the conditions for the anaerobic fermentation process include: applying an external electrode to conduct electricity, and the voltage between the cathode and the anode is greater than 0 V and not greater than 1.5 V.

[0036] Furthermore, the conditions for the anaerobic fermentation process include: applying an external electrode to conduct electricity, and the voltage between the cathode and the anode is greater than 0 V and not greater than 0.9 V.

[0037] It should be noted that moreover, there is an electron transfer medium in the remaining sludge and waste fermentate in the co-fermentate, which has a positive response to the external electrode. Introducing an external microcurrent for electrochemical anaerobic fermentation is beneficial to promoting anaerobic fermentation hydrolysis and acidification to produce acid, and can increase the acid production amount of anaerobic fermentation.

[0038] Preferably, the voltage between the cathode and the anode is 0.9 V.

[0039] Furthermore, the conditions of the anaerobic fermentation process include: the hydraulic retention time is 6 - 7 days, and the sludge retention time is 6 - 7 days.

[0040] It should be noted that controlling the hydraulic retention time and the sludge retention time of the anaerobic fermentation process within the above ranges can inhibit the activity of methanogens, avoid the generation of a large amount of methane, and solve the problem of a large amount of difficult - to - treat methane generated in the prior art after treating excess sludge; on the other hand, the hydraulic retention time mainly reaches the highest value due to acid production in 6 - 7 days, and the sludge retention time of 6 - 7 days can ensure the activity of the excess sludge in the co - fermentation material and the acid - production efficiency. Compared with only using excess sludge for acid - producing fermentation, the sludge retention time is greatly shortened when the present invention uses co - fermentation material for fermentation. Among them, the hydraulic retention time refers to the average residence time of the supernatant, i.e., the fermentation broth, generated by anaerobic fermentation in the fermentation tank; the sludge retention time refers to the average residence time of the excess sludge in the co - fermentation material in the fermentation tank.

[0041] Furthermore, the conditions of the anaerobic fermentation process also include: continuously stirring the co - fermentation material;

[0042] Among them, the stirring speed is 300 - 400 rpm.

[0043] It should be noted that the continuous stirring is non - stop stirring for 24 hours every day;

[0044] Moreover, continuous stirring is beneficial to the mixing of the co - fermentation material and increases the shear force of sludge flocs, which is beneficial to the production of VFAs.

[0045] Furthermore, the conditions of the anaerobic fermentation process also include: the temperature is 25 - 35 °C.

[0046] It should be noted that the temperature condition of the anaerobic fermentation process only needs to be maintained at 25 - 35 °C without special control, which has a wider applicability.

[0047] Furthermore, in step S2, the conditions of the inert gas stripping include: making the oxygen content in the fermentation tank < 0.1% (volume fraction).

[0048] By inert gas stripping, the volume fraction of the oxygen content in the fermentation tank is < 0.1% to achieve an anaerobic environment to ensure the progress of anaerobic fermentation.

[0049] Furthermore, the inert gas is one or two of nitrogen and argon; preferably nitrogen.

[0050] Furthermore, when the anaerobic fermentation method of the present invention is first applied to treat the co - fermentation material, step S1 further includes: introducing starch into the fermentation tank.

[0051] Further, the step S1 includes:

[0052] In the first five days, starch is mixed with the co-ferment and put in. The proportion of starch gradually decreases from 100% on the first day to 0%, and the proportion of the co-ferment gradually increases from 0% on the first day to 100%. Among them, ammonium sulfate and potassium dihydrogen phosphate need to be appropriately supplemented in the first two days to ensure that the ratio of COD:N:P is 100-150:5:1.

[0053] Starting from the sixth day, the co-ferment with a volume of 1 / 6-1 / 7 of the tank body is pumped into the fermentation tank every day.

[0054] It should be noted that when the anaerobic fermentation method is first applied to treat the co-ferment, by adding starch and appropriately supplementing ammonium sulfate and potassium dihydrogen phosphate in the first two days, ensuring that the ratio of COD:N:P is within the above range can obtain a better anaerobic fermentation environment faster.

[0055] Further, during the anaerobic fermentation process, the COD of the substrate is maintained at 10,000 mg / L-30,000 mg / L. Among them, the substrate includes the co-ferment and starch, that is, the sum of the COD of the co-ferment and starch is maintained at 10,000 mg / L-30,000 mg / L. Ensuring that the COD is within the above range is beneficial to anaerobic fermentation to produce acid.

[0056] Further, in step S4, the supernatant contains volatile fatty acids generated during the anaerobic fermentation process.

[0057] It should be noted that the supernatant has a high biological added value and can be used as a carbon source in other sewage treatment processes that require an external carbon source, greatly improving the utilization rate of sludge resources.

[0058] Further, in step S4, the treated sludge includes a small part of the sludge in the supernatant overflowing from the overflow weir and the sludge actively discharged.

[0059] Further, in step S4, the gas can be collected through the three-phase separator at the top of the fermentation tank.

[0060] 3. Beneficial effects

[0061] Adopting the technical solution provided by the present invention, compared with the prior art, it has the following beneficial effects:

[0062] (1) For the co-ferment provided by the present invention, by adjusting the ratio of the auxiliary waste to the excess sludge, the C / N value is 20 / 1-30 / 1, the pH value is 6-9, and the temperature is 20-35 °C, which is beneficial to promoting the hydrolysis and acidification of the excess sludge and generating more volatile fatty acids.

[0063] (2) The anaerobic fermentation method provided by the present invention uses a co-ferment for anaerobic fermentation. By adjusting external conditions and applying an external voltage to promote the electron transfer of the co-ferment, the sludge acclimation time can be significantly shortened, thereby improving the fermentation and acid production efficiency.

[0064] (3) For the anaerobic fermentation method provided by the present invention, continuous stirring is beneficial to the mixing of the co-ferment and increases the shear force of sludge flocs, which is beneficial to the production of VFAs. Description of the Drawings

[0065] Figure 1 It is a graph showing the change of pH over time during the fermentation of the co-ferment under different externally applied voltage conditions in Example 1.

[0066] Figure 2 It is a graph showing the change of TOC over time during the fermentation of the co-ferment under different externally applied voltage conditions in Example 1.

[0067] Figure 3 It is a graph showing the influence of fermentation acid production during the fermentation of the co-ferment under different externally applied voltage conditions in Example 1.

[0068] Figure 4 It is a result graph of the yield and species distribution of acetic acid, propionic acid, butyric acid, and valeric acid, VFAs under different externally applied voltage conditions in Example 1.

[0069] Figure 5 It is a graph showing the influence of different C / N values on the fermentation acid production of the co-ferment under the conditions of Example 2.

[0070] Figure 6 It is a graph showing the influence of different pH values on the fermentation acid production of the co-ferment under the conditions of Example 3.

[0071] Figure 7 It is a graph showing the influence of stirring conditions on the fermentation acid production under the conditions of Example 4. Detailed Embodiments

[0072] The present disclosure can be more easily understood by referring to the following description in conjunction with examples, all of which form a part of the present disclosure. It should be understood that the present disclosure is not limited to the specific products, methods, conditions or parameters described and / or illustrated herein. Further, the terms used herein are for the purpose of describing specific embodiments by way of example only and are not intended to be limiting, unless otherwise specified.

[0073] It should also be understood that, for clarity, certain features of the present disclosure may be described herein in the context of separate embodiments, but may also be provided in combination with each other in a single embodiment. That is, unless clearly incompatible or specifically excluded, each separate embodiment is considered combinable with any other embodiment, and such combination is considered to represent another distinct embodiment. Conversely, for brevity, the various features of the present disclosure described in the context of a single embodiment may also be provided separately or in any sub-combination. Finally, although a particular embodiment may be described as part of a series of steps or part of a more general structure, each step or sub-structure itself may also be considered an independent embodiment.

[0074] Unless otherwise specified, it should be understood that each individual element in a list and each combination of the individual elements in that list will be construed as a different embodiment. For example, a list of embodiments expressed as "A, B, or C" should be construed as including the embodiments "A", "B", "C", "A or B", "A or C", "B or C", or "A, B, or C".

[0075] In the present disclosure, the singular forms of the articles "a", "an", and "the" also include the corresponding plural referents, and a reference to a particular numerical value includes at least that particular value, unless the context clearly dictates otherwise. Thus, for example, a reference to "a substance" is a reference to at least one of such substance and its equivalents.

[0076] When items are described by use of associative terms such as "…… and / or ……", the description should be understood to include any one of the associated listed items and all combinations of one or more of them.

[0077] Generally, the use of the term "about" indicates an approximation that may vary depending on the desired characteristics obtained by the disclosed subject matter and will be interpreted in a context-dependent manner based on functionality. Thus, one of ordinary skill in the art will be able to interpret a certain degree of variance on a case-by-case basis. In some cases, the number of significant digits used in expressing a particular value may be a representative technique for determining the variance allowed by the term "about". In other cases, a gradient within a series of values may be used to determine the range of variance allowed by the term "about". Further, all ranges in the present disclosure are inclusive and combinable, and a reference to a value within a range includes each value within that range.

[0078] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field to which this invention belongs; the terms used herein and / or include any and all combinations of one or more of the associated listed items.

[0079] VFA: The abbreviation of volatile fatty acid, which refers to short-chain fatty acids produced by anaerobic bacteria fermentation under anaerobic conditions and has volatility.

[0080] VFAs: The plural form of VFA, that is, the collective or general term for multiple volatile fatty acids.

[0081] TVFA: Total volatile fatty acid, which is used to represent the total amount of all volatile fatty acids in a certain sample or system.

[0082] In the following examples, those without specific conditions mentioned are carried out according to conventional conditions or conditions recommended by the manufacturer. For reagents or instruments without the manufacturer indicated, they are all conventional products that can be obtained through commercial purchase.

[0083] It should be noted that the fermenter used in the embodiments of the present invention is the sludge fermentation device for targeted acid production in Example 1 of the sludge fermentation method for targeted acid production in the Chinese patent with the publication number CN118325975A. The excess sludge is taken from the secondary sedimentation tank sludge of Fangyang Industrial Wastewater Comprehensive Treatment Center in Lianyun District, Lianyungang City, Jiangsu Province.

[0084] The following specific examples are used to further illustrate the present invention, but the examples do not limit the present invention in any form. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in the technical field. The essential features and remarkable effects of the present invention can be reflected from the following examples. The described examples are part of the examples of the present invention, rather than all of them. Therefore, they do not limit the present invention. Those skilled in the art make some non-essential improvements and adjustments based on the content of the present invention, which all fall within the protection scope of the present invention.

[0085] Example 1

[0086] This example explored the optimal applied external voltage for anaerobic fermentation to produce acid, including the following steps:

[0087] Pretreatment: In the first five days, starch and co-ferment were mixed and put into the fermenter. The mass ratio of starch gradually decreased from 100% on the first day to 0%, and the mass ratio of co-ferment gradually increased from 0% on the first day to 100%. Ammonium sulfate and potassium dihydrogen phosphate were appropriately supplemented in the first two days to ensure that the ratio of COD:N:P was 100 - 150:5:1. The specific dosage of different substances in the first five days is shown in Table 1. Among them, in this example, the co-ferment was obtained by mixing excess sludge and corn straw, and the C / N value of the co-ferment was 25, the pH value was 6.5, and the temperature was 25°C; the corn straw was pulverized before mixing, and the particle size after pulverization was 1 - 5 mm.

[0088] Table 1 Dosage of different substances in the first five days

[0089] starch co-ferment ammonium sulfate potassium dihydrogen phosphate the first day 100％ 0％ appropriate amount appropriate amount the second day 80％ 20％ appropriate amount appropriate amount the third day 60％ 40％ 0g 0g the fourth day 40％ 60％ 0g 0g the fifth day 20％ 80％ 0g 0g the sixth day and after 0％ 100％ 0g 0g

[0090] Step 1: Pump the co-ferment into the fermenter, and the pumping volume is 1 / 6 of the volume of the fermenter.

[0091] Step 2: Blow off nitrogen in the fermenter for 3 min, so that the oxygen content in the fermenter is <0.1% (volume fraction) to achieve an anaerobic environment to ensure the progress of anaerobic fermentation.

[0092] Step 3: Conduct anaerobic fermentation in the fermenter. The conditions during the anaerobic fermentation process include: the temperature is 25 - 35 °C; the stirring speed is 300 rpm; the sum of the COD of starch and co-ferment during the anaerobic fermentation process is kept at 10000 mg / L - 30000 mg / L;

[0093] In this embodiment, applied voltages of 0.3 V, 0.6 V, 0.9 V, 1.2 V, and 1.5 V are set as the conditions for anaerobic fermentation.

[0094] Index analysis:

[0095] In this embodiment, the supernatant is collected from the first sampling port as a liquid sample, and the changes in various indexes such as the pH value, conductivity, redox potential, and temperature of the liquid sample are monitored for 30 days;

[0096] It includes: taking 8 mL of supernatant every day, centrifuging at 8000 r / min for 5 min, filtering by suction using a microporous filter membrane with a pore size of 0.45 μm, and using GC-MS to measure acetic acid, propionic acid, butyric acid, and valeric acid, the production and species distribution of VFAs; diluting the supernatant by 10 times and detecting COD by the method of rapid digestion spectrophotometry; diluting by 100 times and using a TOC analyzer to detect TOC (total organic carbon).

[0097] Sampling is carried out from the bottom sludge discharged every day for monitoring;

[0098] It includes: taking bottom sludge every day, detecting TS and VS, taking out a part and storing it in the refrigerator at a temperature of -20 °C, then detecting, and extracting EPS (extracellular polymeric substances) every 5 days and detecting 3D-EEM (three-dimensional fluorescence spectroscopy).

[0099] Combined with Figure 1 , it can be intuitively seen that under the condition of 0.9 V voltage, the pH value of the reactor decreases faster, indicating that under the stimulation of 0.9 V voltage, acid-producing bacteria can play a greater role.

[0100] Combined with Figure 2 , in the figure, under the condition of 0.9 V voltage, the growth rate of TOC is the highest, indicating that under the condition of 0.9 V voltage, more substances in the sludge are converted into acids, so the acid production is higher.

[0101] Combined Figure 3 , the line chart of the total acid production can be visually seen. The total acid production is higher under the condition of 0.9V, indicating that 0.9V is a more suitable voltage for co-fermentation acid production.

[0102] Combined Figure 4 , the yields of acetic acid, propionic acid, butyric acid, and valeric acid under different voltage conditions can be visually seen. The acid production of the reactor and the acetic acid production are higher under the condition of 0.9V, indicating that 0.9V is a more suitable voltage for acetic acid production in co-fermentation acid production.

[0103] Example 2

[0104] In this example, the C / N value of the anaerobic co-ferment was explored. The steps were basically the same as those in Example 1, with the only difference being:

[0105] The first step: The sieved excess sludge and bagasse were mixed as the co-ferment. Among them, the bagasse was pulverized before mixing, and the particle size after pulverization was 1-5 mm; the excess sludge and bagasse were mixed in different proportions to obtain co-ferments with different C / N values, and the pH values of the co-ferments with different C / N values were maintained at 7 and the temperature was 25 °C;

[0106] The third step: The applied voltage in the anaerobic fermentation conditions was 0.9V.

[0107] Meanwhile, the index analysis was basically the same as that in Example 1.

[0108] Figure 5 The medium acid production rate is the volatile fatty acid production rate, and the acetic acid production rate is the production rate calculated in terms of acetic acid equivalent. The ratio represents the efficiency of the substrate being converted into volatile fatty acids. From Figure 5 it can be seen that when the C / N value is 20-30, the acetic acid production is higher, and the acid production is also at a relatively high level.

[0109] Example 3

[0110] In this example, the pH value of the anaerobic co-ferment was explored. The steps were basically the same as those in Example 1, with the only difference being:

[0111] The first step: The excess sludge (WAS), corn straw (CS), and pig manure (PM) were treated and combined into four co-ferments. Among them, the corn straw and pig manure were pulverized before mixing, and the particle size after pulverization was 1-5 mm; they were respectively: ① 1 L of enzymatically hydrolyzed WAS, 31 g of sieved CS, and 5 g of sieved PM; ② 1 L of enzymatically hydrolyzed WAS and 25.5 g of sieved CS; ③ 1 L of enzymatically hydrolyzed WAS; ④ 1 L of fresh WAS. The pH values of the four obtained co-ferments were all 6.9, the C / N values were all 25, and the temperatures were all 30 °C, and they were respectively pumped into the fermentation tank.

[0112] Step 3: Set the applied voltage in the anaerobic fermentation condition to 0.9V.

[0113] As Figure 6 shown, mainly analyze the microbial community, draw the correlation between the bacterial community composition and environmental variables during the co-fermentation of four co-fermentants, and find that adjusting the ORP (oxidation-reduction potential) in the range of -380 to -320 mV promotes the accumulation of VFAs when the pH is 6.5 - 7.5.

[0114] Example 4

[0115] This example explores whether stirring is required during the anaerobic fermentation process. The steps are basically the same as those in Example 1, except that:

[0116] Step 1: Only use excess sludge and add the excess sludge into eight fermentation tanks respectively;

[0117] Step 3: The conditions of the eight fermentation tanks are as follows: ① The static fermentation tank ferments at room temperature of 25°C for one day; ② The static fermentation tank ferments at 30°C for one day; ③ The completely mixed fermentation tank ferments at room temperature of 25°C for one day; ④ The completely mixed fermentation tank ferments at 30°C for one day; ⑤ The static fermentation tank ferments at room temperature of 25°C for 3 days; ⑥ The static fermentation tank ferments at 30°C for 3 days; ⑦ The completely mixed fermentation tank ferments at room temperature of 25°C for three days; ⑧ The completely mixed fermentation tank ferments at 30°C for three days; The applied voltage in the anaerobic fermentation condition is 0.9V, and measure the content of SCOD (soluble chemical oxygen demand) in the supernatant; and no applied voltage is applied. Among them, the complete mixing in this example means continuous mixing.

[0118] The final results are as Figure 7 shown, adding stirring can promote the hydrolysis and acidification of excess sludge and increase the acid production in the system.

Claims

1. A co-ferment, characterized in that: It includes excess sludge and auxiliary waste; The auxiliary waste includes at least one of food waste and agricultural waste; Wherein, the C / N value of the co-ferment is 20 / 1 to 30 / 1.

2. The co-ferment according to claim 1, characterized in that: The pH value of the co-ferment is 6.0 to 9.0; The temperature of the co-ferment is 20.0 to 35.0 °C.

3. An anaerobic fermentation method using the co-ferment as described in any one of claims 1 to 2, characterized in that, It includes the following steps: S1. Feed the co-ferment into a fermentation tank; S2. Blow off the inside of the fermentation tank with inert gas; S3. Conduct anaerobic fermentation in the fermentation tank, and apply an external electrode to conduct electricity during the anaerobic fermentation process; S4. Collect the treated sludge, supernatant and gas.

4. The anaerobic fermentation method according to claim 3, characterized in that: The voltage between the cathode and the anode is greater than 0V and not greater than 1.5V.

5. The anaerobic fermentation method according to claim 3, characterized in that: The voltage between the cathode and the anode is greater than 0V and not greater than 0.9V.

6. The anaerobic fermentation method according to any one of claims 3 to 5, characterized in that: The conditions of the anaerobic fermentation process include: the hydraulic retention time is 6 to 7 days, and the sludge retention time is 6 to 7 days.

7. The anaerobic fermentation method according to claim 6, characterized in that: The conditions of the anaerobic fermentation process further include: continuously stirring the co-ferment.

8. The anaerobic fermentation method according to claim 7, characterized in that: The rotation speed of the stirring is 300 to 400 rpm.

9. The anaerobic fermentation method according to claim 8, characterized in that: In step S2, the conditions of the inert gas blow-off include: making the volume fraction of oxygen content in the fermentation tank <0.1%.

10. The anaerobic fermentation method according to claim 3, characterized in that: Step S1 further includes: feeding starch into the fermentation tank.

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