Method for promoting anaerobic fermentation of sludge to produce acid

Abstract

The invention provides a method for promoting anaerobic fermentation of sludge to produce acid, which comprises the following steps: pretreating sludge to obtain pretreated sludge; a certain amount of orange peel and a microbial agent capable of decomposing cellulose and prolonging a carbon chain are added into the pretreated sludge, co-fermentation anaerobic acid production is performed, and in the pretreatment step, the pH value of the sludge is adjusted to 5.5-6.0, and water bath heating is performed at a preset temperature. According to the method disclosed by the invention, the anaerobic fermentation process of the sludge is optimized, and the yield of medium-chain fatty acid is remarkably increased.

Description

Technical Field

[0001] The present invention relates to the technical fields of environmental engineering and microbial fermentation, and particularly relates to a method for promoting anaerobic fermentation of sludge to produce fatty acids. Background Art

[0002] At present, due to reasons such as the continuous growth of the population, the continuous advancement of the industrialization process, and the increasing living standards, not only in China but also the whole world is facing crises such as water resource shortage and water environmental pollution. The rapid industrialization, urbanization, and population growth have led to a sharp increase in water use and sewage discharge. Semi-solid or solid substances with different moisture contents are generated in multiple links of sewage treatment, which are the "by-products" that cannot be avoided in current sewage treatment - sludge, containing various toxic and harmful substances. If not properly treated, it will pose a serious threat to the environment and the ecosystem. Therefore, the effective management and resource utilization of sludge have become urgent problems to be solved.

[0003] Since the last century, anaerobic fermentation of sludge has gradually become the focus of global research. This process is generally considered to include four key stages, namely the hydrolysis stage, the acidification stage, the acetic acid production stage, and the methane production stage. Volatile fatty acid (VFA) is an organic acid, which is a product in the process of anaerobic fermentation of sludge, is soluble in the fermentation broth and easy to recover, and has a relatively high added value. This organic acid can be used as a source of external carbon nutrition for microorganisms in the process of sewage treatment (for example, when the influent COD is insufficient) after a series of treatments, improving the removal effect of nutrient elements in sewage. Therefore, studying the production of fatty acids by sludge fermentation is one of the very promising ways.

[0004] It should be noted that the information disclosed in the above background art part is only used to enhance the understanding of the background of the present invention. Therefore, it may include information that does not constitute the prior art known to those skilled in the art. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for promoting anaerobic fermentation of sludge to produce acid by combining low-temperature pyrolysis with orange peel, which is simple to operate, can significantly increase the acid production amount of sludge, realize the resource utilization of sludge, and at the same time can greatly reduce waste.

[0006] The method for promoting anaerobic fermentation of sludge to produce acid according to the present invention may include the following treatment steps:

[0007] Pretreat the sludge to obtain pretreated sludge;

[0008] Add a certain amount of orange peel and a microbial agent with the function of decomposing cellulose and extending the carbon chain to the pretreated sludge, and then carry out co-fermentation anaerobic acid production.

[0009] Among them, the steps of the pretreatment include: adjusting the pH value of the sludge to the range of 5.5 - 6.0 and performing water bath heating at a predetermined temperature.

[0010] According to an embodiment of the present invention, the microbial inoculum includes Klebsiella oxytoca, Clostridium pasteurianum, and Bacillus stearothermophilus.

[0011] According to an embodiment of the present invention, the concentration of Klebsiella oxytoca in the microbial inoculum is 5×10 5 ~3.5×10 7 CFU / mL, the concentration of Clostridium pasteurianum in the microbial inoculum is 2×10 5 ~1.5×10 7 CFU / mL, and the concentration of Bacillus stearothermophilus in the microbial inoculum is 1×10 5 ~1×10 7 CFU / mL.

[0012] According to an embodiment of the present invention, the proportion of the microbial concentration of Klebsiella oxytoca in the microbial inoculum is 50% - 70%.

[0013] According to an embodiment of the present invention, Klebsiella oxytoca, Clostridium pasteurianum, and Bacillus stearothermophilus are compounded in a ratio of 5:4:1, 6:3.3:0.7, 6.5:2.1:1.4, or 7:2:1 to form the microbial inoculum.

[0014] According to an embodiment of the present invention, the concentration of the microbial inoculum added to the pretreated sludge is 1×10 6 ~5×10 7 CFU / mL.

[0015] According to an embodiment of the present invention, the addition amount of the orange peel is calculated based on the concentration of D-limonene, and the concentration range of D-limonene in the pretreated sludge is 0.5 - 3 mg / g MLSS.

[0016] According to an embodiment of the present invention, the mass ratio of the orange peel to the pretreated sludge is 0.05:1 - 0.6:1.

[0017] According to an embodiment of the present invention, the concentration of the pretreated sludge is 2 - 8 g / L MLSS.

[0018] According to an embodiment of the present invention, the sludge is the excess sludge generated from the secondary sedimentation tank of a sewage treatment plant and is obtained by natural sedimentation at 4°C for more than 12 hours.

[0019] According to an embodiment of the present invention, the treatment process of the anaerobic environment includes: introducing an inert gas such as nitrogen, argon, helium or neon into the fermentation reaction vessel for at least 5 minutes.

[0020] According to an embodiment of the present invention, the pretreatment time can be 1 hour, and the above-mentioned predetermined temperature can be 90 ± 0.5 °C.

[0021] According to an embodiment of the present invention, before anaerobic fermentation to produce acid, the pH of the pretreated sludge is adjusted to between 6.0 and 7.0.

[0022] According to an embodiment of the present invention, the time for anaerobic fermentation to produce acid is 8 - 10 d, and the temperature is 35 ± 0.5 °C.

[0023] The beneficial effects of the present invention are as follows:

[0024] Through the synergistic metabolism of D-limonene in orange peel and the composite microbial agent, the present invention activates the activity of carbon chain elongation enzyme, increasing the MCFA yield by 50% - 80% and breaking through the bottleneck of traditional processes.

[0025] The present invention uses waste orange peel as a natural promoter, combined with low-temperature pyrolysis pretreatment of sludge, to achieve "treating waste with waste", reducing treatment costs while reducing agricultural and sludge pollution, and realizing the reduction and resource utilization of sludge. Description of the Drawings

[0026] In order to more clearly illustrate the technical solutions in the embodiments of this specification or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments recorded in the embodiments of this specification. For those of ordinary skill in the art, other drawings can also be obtained based on these drawings.

[0027] Figure 1 It is the influence of the concentration of pretreated sludge on the accumulation amount of MCFA, and the line graph of the accumulation amount of MCFA with the fermentation time. Detailed Embodiments

[0028] The technical solutions in the embodiments of the present invention will be elaborated in detail and clearly with reference to the drawings. Obviously, the discussed embodiments only represent some application scenarios of the present invention and do not cover all possible implementation manners. The description of at least one exemplary embodiment should be regarded as explanatory rather than a limitation of the present invention and its potential applications or uses.

[0029] Based on the present invention, any similar products created by being inspired by the present invention or by combining the present invention with the prior art, whether exactly the same or having similar characteristics, are considered to be included within the protection scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

[0030] The present invention provides a method for promoting anaerobic fermentation of sludge to produce acid, which method comprises: pretreating the sludge to obtain pretreated sludge; and adding a certain amount of orange peel and a microbial inoculant capable of decomposing cellulose and extending the carbon chain to the pretreated sludge for co-fermentation anaerobic acid production. Among them, the steps of pretreatment include: adjusting the pH value of the sludge to within the range of 5.5 - 6.0, and performing water bath heating at a predetermined temperature.

[0031] Orange peel contains D-limonene, and D-limonene can affect the anaerobic digestion process. Specifically, D-limonene can improve the synthesis efficiency of medium-chain fatty acids through co-metabolism with a microbial inoculant capable of decomposing cellulose and extending the carbon chain. At the same time, the pretreatment of the sludge can destroy the cell wall structure of the sludge, release intracellular organic matter, and after adding the above-mentioned microbial inoculant, it can further hydrolyze macromolecular proteins to provide high-concentration soluble substrates for subsequent acid-producing bacteria. The synergistic effect of this pretreatment and functional bacteria makes the co-metabolism efficiency of D-limonene and Klebsiella oxytoca for acid production increase by more than 30%.

[0032] According to the embodiments of the present invention, the microbial inoculant capable of decomposing cellulose and extending the carbon chain may include Klebsiella oxytoca, Clostridium pasteurianum, and Bacillus stearothermophilus. In an anaerobic environment, D-limonene can be decomposed by Klebsiella oxytoca into intermediate products such as α-terpineol and geraniol. These substances can not only participate directly in fatty acid synthesis as carbon sources, but also activate the gene expression of acyl-CoA dehydrogenase and thioesterase in the bacterial cells, promoting the chain extension and release of medium-chain fatty acids. At the same time, the reduced coenzyme (NADH) produced by the metabolism of Klebsiella oxytoca can provide an electron donor for Clostridium pasteurianum, forming an inter-species electron transfer network, thereby strengthening the accumulation of medium-chain fatty acids such as butyric acid and caproic acid. In addition, Bacillus stearothermophilus in the microbial inoculant can secrete heat-resistant protease to achieve the hydrolysis of macromolecular proteins and provide high-concentration soluble substrates.

[0033] According to the embodiments of the present invention, the concentration of Klebsiella oxytoca in the microbial inoculant can be 5×10 5 ~3.5×10 7 CFU / mL, and the concentration of Clostridium pasteurianum in the microbial inoculant can be 2×105 ~1.5×10 7 CFU / mL, the concentration of the Bacillus stearothermophilus in the microbial inoculant can be 1×10 5 ~1×10 7 CFU / mL. When their concentrations in the microbial inoculant are within the above numerical range, the three bacteria can synergistically and efficiently decompose organic matter, significantly increase the production of volatile fatty acids, and inhibit the activity of methanogens.

[0034] According to an embodiment of the present invention, the concentration of the microbial inoculant added to the pretreated sludge is 1×10 6 ~5×10 7 CFU / mL. When the addition concentration of the microbial inoculant is within this range, it can efficiently decompose the sludge organic matter and shorten the fermentation cycle.

[0035] According to an embodiment of the present invention, the proportion of the microbial concentration of Klebsiella oxytoca in the microbial inoculant can be 50% - 70%. When the proportion of the concentration of Klebsiella oxytoca in the microbial concentration of the microbial inoculant is 50% - 70%, in this case, when Klebsiella oxytoca accounts for 50% - 70%, it dominates acid production and has an obvious promoting effect on acid production.

[0036] According to an embodiment of the present invention, the concentration of the microbial composite inoculant added to the pretreated sludge can be 1×10 6 ~5×10 7 CFU / mL.

[0037] In addition, preferably, the concentration range of D-limonene in the pretreated sludge can be 0.5 - 3 mg / g MLSS.

[0038] According to an embodiment of the present invention, the mass ratio of orange peel to pretreated sludge can be 0.05:1 - 0.6:1. In this case, the addition amount of orange peel can provide sufficient D-limonene to inhibit methanogens, and the orange peel can optimize the system pH as a carbon source to achieve efficient acid production.

[0039] According to an embodiment of the present invention, the sludge can be the excess sludge generated from the secondary sedimentation tank of a sewage treatment plant and obtained by natural sedimentation at 4°C for more than 12 h. According to the embodiment, the concentration of the sludge can be 2 - 8 g / L MLSS. If the sludge concentration is too low, it will lead to insufficient anaerobic fermentation microorganisms; if the sludge concentration is too high, it will affect the mass transfer rate between substances and the fermentation acid production rate.

[0040] In addition, the treatment process of the anaerobic environment during co-fermentation anaerobic acid production can include: introducing an inert gas such as nitrogen, argon, helium or neon into the fermentation reaction vessel for at least 5 minutes.

[0041] The pre-treatment time can be 1 hour, and the above-mentioned predetermined temperature can be 90 ± 0.5 °C.

[0042] According to an embodiment of the present invention, before anaerobic fermentation for acid production, the pH value of the pre-treated sludge is adjusted to between 6.0 and 7.0.

[0043] According to an embodiment of the present invention, the time for anaerobic fermentation for acid production is 8 - 10 d, and the temperature can be 35 ± 0.5 °C.

[0044] The experimental implementation steps of the embodiments and comparative examples of the present invention are as follows:

[0045] Take the secondary sedimentation tank sludge from the sewage treatment plant, let it settle naturally at 4 °C for 12 hours, remove the supernatant, concentrate it to a sludge concentration of 2 - 8 g / L MLSS, adjust the pH value of the obtained sludge to 5.5 - 6.0 with dilute hydrochloric acid or sodium hydroxide solution, place the adjusted sludge in a constant temperature water bath at 90 ± 0.5 °C and heat it for 1 hour to complete the hydrothermal pretreatment, adjust the pH value of the pre-treated sludge to 6.0 - 7.0, and set aside. Dry and crush the orange peel to a particle size of ≤ 1 mm, add it to the pre-treated sludge according to a mass ratio of 0.05:1 - 0.6:1 (orange peel:sludge), mix Klebsiella oxytoca (50% - 70%), Clostridium pasteurianum, and Bacillus stearothermophilus in proportion, and the total concentration of the microbial agent is 1×10 6 ~5×10 7 CFU / mL. Add the microbial agent to the pre-treated sludge and mix evenly. Transfer the mixed sludge to a sealed fermentation tank, introduce inert gases such as nitrogen and argon for at least 5 minutes to ensure an anaerobic environment, and carry out anaerobic fermentation under a constant temperature condition of 35 ± 0.5 °C for 8 - 12 days.

[0046] In the following experiments, in each table, the inventors only selectively listed some experimental data as examples. For example, in Table 1, the sludge concentration was listed as a variable for experimental groups A1 - A4, while the microbial agent concentration, the mass ratio of orange peel to sludge, the proportion of Klebsiella oxytoca, and the composition of other strains were only listed as examples with values close to the middle of the corresponding ranges.

[0047] However, in fact, the inventors also selected various microbial agent concentrations (i.e., 1×10 6 ~5×10 7Other values within the range of CFU / mL), various mass ratios of orange peel to sludge (i.e., other values within the range of 0.05:1 to 0.6:1), different proportions of Klebsiella oxytoca (other values within the range of 50% to 70%), and other species compositions with different ratios (other proportional relationships between Clostridium pasteurianum and Bacillus stearothermophilus) were used as fixed quantities, and only the sludge concentration was used as a variable for experiments. The results of these experimental data were similar to the results of the experimental data listed in Table 1. Therefore, since the experimental data and results in Table 1 (as Figure 1 shown) can clearly express the influence of sludge concentration changes on the experimental results, only these values were selected as examples and listed in Table 1. However, those skilled in the art should understand that other experimental results within the above range also conform to the experimental results in Table 1, that is, the description of the experimental results in Table 1 also applies to other data within the above range.

[0048] The situations of Tables 2 to 4 are similar to Table 1, so their detailed descriptions are omitted. In addition, in the experiments of the co-variation of multiple variables in Table 5, some endpoint value experimental data within the above range were further selected as examples and listed to further verify the rationality of the selected value range.

[0049] Table 6 shows the comparative examples of the above experimental examples. In each experimental group of the comparative examples, at least one data is not within the above range of this application. Similar to Tables 1 to 5, Table 6 also only shows some experimental data, that is, only shows some situations where the data are not within the above range of this application as examples of the comparative examples. However, those skilled in the art should understand that other experimental results not within the above range of this application also conform to the experimental results in Table 6.

[0050] 1. Sludge concentration gradient group (other parameters fixed)

[0051] Table 1

[0052]

[0053]

[0054] 2. Bacterial agent concentration gradient group (other parameters fixed) Table 2

[0055]

[0056] 3. Mass ratio gradient group (other parameters fixed) Table 3

[0057]

[0058]

[0059] 4. Proportion gradient group of Klebsiella oxytoca (other parameters fixed) Table 4

[0060]

[0061] 5. Combined Example Groups (Multivariable Synergistic Verification)

[0062] Table 5

[0063]

[0064]

[0065] 6. Comparative Example Groups

[0066] Table 6

[0067]

[0068]

[0069] 7. Comparative Example Groups (Missing Key Steps or Ingredients, Other Parameters Set According to Example A1)

[0070] Comparative Example G1: Do not add microbial inoculant;

[0071] Comparative Example G2: Do not add orange peel, only carry out sludge fermentation.

[0072] The examples verified the rationality of the process conditions in the claims through multi-dimensional parameter combinations, revealing the influence law of various factors on the production of medium-chain fatty acids (MCFAs); the comparative examples clarified the critical values and necessity of the process parameters in the claims through extreme parameter settings.

[0073] Figure 1 The figure showing the change in the accumulation amount of MCFA with fermentation time for the sludge concentration gradient groups (A1 - A5) and the comparative example F groups (F1 and F2) and the comparative example G groups was given. The sludge concentration directly affects the substrate supply and the microbial metabolic balance. When the sludge concentration ranges from 2 g / L to 8 g / L (A1 - A5), the MCFA production first increases and then stabilizes with the increase of the concentration. When the sludge concentration is 5 g / L (A3), the acid production is the highest (1280 mg / L). Comparative examples F1 (1 g / L) and F2 (9 g / L) show that when the concentration is too low, the hydrolysis products of the sludge are not sufficient to support the metabolism of the microbial community, resulting in the stagnation of the acidification stage and a decrease in acid production. When the concentration is too high, the sludge viscosity increases, inhibiting the diffusion of the inoculant and the synthesis of medium-chain fatty acids. This result verifies that the sludge concentration of 2 - 8 g / L specified in the patent is the optimal range.

[0074] Under the condition of the same sludge concentration, compared with Group G and F1 and F2 of Comparative Example F group, the accumulation effect of MCFA in Group A is significantly better, and the highest MCFA concentration can reach 850 mg / L. At the same time, the overall increase rate of MCFA during the co-fermentation of orange peel and sludge is higher, and the peak value can be reached on the tenth day of fermentation, indicating that the overall effect of adding the necessary component microbial inoculant and co-fermenting orange peel and sludge is better.

[0075] In terms of the change of MCFA content in Group A, F1 and F2 of Comparative Example F group, and Comparative Example G group, the experimental results are visually presented in the form of a line chart to more clearly compare the dynamic changes of key indicators under different conditions. For the microbial inoculant concentration gradient group (Group B), mass ratio gradient group (Group C), proportion gradient group of Klebsiella oxytoca (Group D), combined example group (Group E) and the remaining comparative example groups (Group F), their fermentation effects are described in detail in words to show the influence of each variable on the fermentation process and products.

[0076] In the experiment of the microbial inoculant concentration gradient group (B1 - B6), the total concentration of the microbial inoculant (1×10 6 ~5×10 7 CFU / mL) needs to match the synergistic effect of D-limonene. As the concentration of the microbial inoculant increases from 1×10 6 to 5×10 7 CFU / mL, the MCFA production shows a trend of first increasing and then slightly decreasing, and the MCFA production is the largest when the concentration of the microbial inoculant is 3×10 7 CFU / mL. In Comparative Example F3 (10 5 CFU / mL), the metabolic intensity of the microbial community is insufficient, and the microbial community cannot form a stable metabolic network, resulting in the interruption of NADH electron transfer, and the acid production is only 36% of the optimal group; in Comparative Example F4 (6×10 7 CFU / mL), due to the excessive competition of bacteria for carbon sources, the bacteria autolyze and release endotoxins, inhibiting the activity of acyltransferase, and the acid production decreases by 50%. It is verified that the microbial inoculant concentration specified in the patent within the range of 1×10 6 ~5×10 7 CFU / mL can achieve better fermentation effects.

[0077] In the mass ratio gradient experiment (C1 - C5), the mass ratio of orange peel to sludge (0.05 - 0.6:1) determines the supply amount of D-limonene. In Comparative Example F5 (0.01:1), due to the lack of D-limonene, acyl-CoA dehydrogenase cannot be effectively activated; in Comparative Example F6 (0.7:1), the excessive D-limonene produces an antibacterial effect, and the acid production decreases by 38%. It shows that the co-fermentation of orange peel and waste sludge has an obvious promoting effect on acid production.

[0078] In the experiment on the proportion gradient of Klebsiella oxytoca (D1 - D4), as the proportion of Klebsiella oxytoca increased from 50% to 70%, the accumulation of MCFA showed a trend of first increasing and then decreasing. When the proportion of Klebsiella oxytoca was too low (Group F7, 40%), its role in the microbial flora was not significant, and it could not fully play the promoting role in fermentation, resulting in a low accumulation of MCFA. When the proportion of Klebsiella oxytoca was too high (Group F8, 100%), due to the lack of cooperation of other strains, the microbial community structure was unbalanced, and efficient fermentation could not be achieved. Control groups F9, F10, and F11 were set up to remove Clostridium pasteurianum, Bacillus licheniformis, and Klebsiella oxytoca respectively. During the experiment, the change in the accumulation of MCFA was abnormal. The rising speed in the early stage was unstable, and there was a downward trend in the later stage, and it could not be stabilized within a reasonable range. The fermentation effect was far worse than that of the normal experimental group, fully reflecting the serious negative effect of the absence of key strains on the co-fermentation of orange peel and sludge. This result verifies the importance of maintaining the balance of the microbial flora and promoting the accumulation of MCFA during the co-fermentation of orange peel and sludge when the proportion of Klebsiella oxytoca is in the range of 50% - 70% and the strains are reasonably matched.

[0079] The combined example groups (E1, E2, E3, E4, E5) carried out experiments within the specified range of multiple parameter combinations. The E groups all obtained relatively high MCFA accumulation. The experiments of the E groups fully showed that when each parameter was combined according to the numerical range of this application, the synergistic optimization of the co-fermentation of orange peel and sludge could be achieved, comprehensively improving the quality and performance of the fermentation products.

[0080] In summary, the optimal effect can be obtained when the reaction conditions are controlled at the following parameters: the sludge concentration is 2 - 8 g / L, the total concentration of the microbial agent is 1×10 6 ~5×10 7 CFU / mL, the mass ratio of orange peel to sludge is 0.05 - 0.6:1, and the proportion of Klebsiella oxytoca is 50% - 70%.

[0081] The present invention uses the natural component D-limonene in orange peel as the key promoter, solves the problem of the accumulation of citrus agricultural waste, and promotes the circular economy model of "treating waste with waste". Through the synergistic effect of low-temperature pyrolysis pretreatment (90°C) combined with a specific microbial agent, the bottleneck of low acid production efficiency and long cycle in traditional sludge anaerobic fermentation is broken through, and the production of medium-chain fatty acids is increased by 50% - 80%, providing an efficient and low-energy-consuming technical path for sludge resource utilization. Compared with traditional sludge landfill or incineration, this process greatly reduces greenhouse gas emissions and the risk of secondary pollution; with the advantages of low cost, simple operation, and strong stability, it can be seamlessly connected to the existing sewage treatment plant facilities, opening up a high-value product market for the sludge treatment industry, enhancing economic benefits while alleviating environmental pressure.

[0082] In summary, through cross-field technology integration, the present invention realizes the synergistic effect of waste resource utilization, pollution control and green production, which has milestone significance for promoting the development of environmental engineering, bio-manufacturing and circular economy industries.

[0083] The specific embodiments described above further elaborate on the purpose, technical solutions and beneficial effects of the present invention. It should be understood that the above description is only the specific embodiments of the present invention and is not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for promoting acid production in anaerobic sludge fermentation, characterized in that, The method includes the following steps: Pretreat the sludge to obtain pretreated sludge; Add a certain amount of orange peel and a microbial agent capable of decomposing cellulose and extending the carbon chain to the pretreated sludge, and then carry out co-fermentation for anaerobic acid production; Among them, the steps of the pretreatment include: adjusting the pH value of the sludge to the range of 5.5-6.0, and carrying out water bath heating at a predetermined temperature.

2. The method for promoting acid production by anaerobic fermentation of sludge according to claim 1, wherein The microbial agent includes Klebsiella oxytoca, Clostridium pasteurianum, and Bacillus stearothermophilus.

3. The method for promoting anaerobic fermentation of sludge to produce acid according to claim 2, wherein The concentration of Klebsiella oxytoca in the microbial agent is 5×105~3.5×107CFU / mL, the concentration of Clostridium pasteurianum in the microbial agent is 2×105~1.5×107CFU / mL, and the concentration of Bacillus stearothermophilus in the microbial agent is 1×105~1×107CFU / mL.

4. The method for promoting acid production by anaerobic fermentation of sludge according to claim 3, wherein, The proportion of the microbial concentration of Klebsiella oxytoca in the microbial agent is 50%~70%.

5. The method for promoting anaerobic fermentation of sludge to produce acid according to claim 4, wherein The Klebsiella oxytoca, the Clostridium pasteurianum, and the Bacillus stearothermophilus are compounded in the ratios of 5:4.2:0.8, 6:3.3:0.7, 6.5:2.1:1.4, and 7:2:1 to form the microbial agent.

6. The method for promoting acid production by anaerobic fermentation of sludge according to any one of claims 2-5, characterized in that The concentration of the microbial agent added to the pretreated sludge is 1×106~5×107CFU / mL.

7. The method for promoting anaerobic fermentation of sludge to produce acid as described in claim 1, characterized in that, The addition amount of the orange peel is calculated based on the concentration of D-limonene, and the concentration range of D-limonene in the pretreated sludge is 0.5~3mg / gMLSS.

8. The method for promoting acid production in anaerobic sludge fermentation according to claim 1, characterized in that The mass ratio of the orange peel to the pretreated sludge is 0.05:1~0.6:

1.

9. The method for promoting anaerobic fermentation of sludge to produce acid according to claim 1, wherein The concentration of the pretreated sludge is 2~8g / L MLSS.

10. The method for promoting acid production by anaerobic fermentation of sludge according to claim 1, wherein The predetermined temperature is 90±0.5℃.

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