Method for enhancing production of fatty acid by anaerobic fermentation of sludge based on sulfate synergistic electron transfer

Abstract

The invention discloses a method for enhancing production of fatty acid by anaerobic fermentation of sludge based on sulfate synergistic electron transfer. The method comprises the following steps: placing residual sludge and inoculated sludge in an anaerobic fermentation device, uniformly stirring and mixing, and then adjusting the initial pH value; then adding a sulfate solution, and continuously stirring and uniformly mixing at 20-25 DEG C; removing oxygen in the anaerobic fermentation device with nitrogen, and sealing the anaerobic fermentation device; and carrying out anaerobic fermentation in a constant-temperature shaking table. By introducing sulfate, sludge flocs and cell structures can be effectively destroyed, the hydrolysis process is remarkably enhanced, and organic matter release is promoted. Meanwhile, sulfate serves as an electron acceptor to mediate electron transfer, efficient conversion of organic matter to the short-chain fatty acid is promoted, and therefore the yield of the short-chain fatty acid is remarkably increased. The method is easy and convenient to operate and remarkable in strengthening effect and has a good application prospect.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of sludge resource utilization, and particularly relates to a method for enhancing sludge anaerobic fermentation to produce fatty acids based on sulfate coordination electron transfer. BACKGROUND

[0002] With the continuous acceleration of urbanization and the rapid development of modern industry and agriculture, the demand for sewage treatment continues to rise, and the resulting sludge production also shows explosive growth. As a byproduct of the sewage treatment process, sludge is rich in organic matter, pathogenic microorganisms, and harmful components such as heavy metals. If not properly disposed of, it can easily cause secondary pollution of groundwater and soil, damage the ecological environment, and even threaten human health. At the same time, the high cost of sludge treatment and disposal has become an important bottleneck restricting the sustainable operation of sewage plants, greatly increasing the economic burden and causing a series of social concerns and management problems. Therefore, how to achieve efficient, economic, and environmentally friendly disposal of sludge has become a technical problem that needs to be solved. Traditional sludge treatment methods such as sanitary landfill and incineration, while alleviating the problem of sludge accumulation to some extent, also expose many drawbacks. Sanitary landfill can easily lead to leachate leakage, polluting groundwater, and there is a risk of fire or explosion during the landfill process; incineration can release harmful gases, causing air pollution. With the increasing strictness of environmental protection requirements and the deepening of the concept of resource recycling, it is difficult to rely solely on traditional disposal methods. Under this background, sludge resource utilization has become the focus of research and industry. In recent years, the technology of anaerobic fermentation of excess sludge to produce acids has gradually emerged, and short-chain fatty acids (SCFAs, mainly including acetic acid, propionic acid, butyric acid, etc.) as high-value products show great resource utilization potential. However, the efficiency of existing excess sludge anaerobic fermentation to produce SCFAs is generally low, with a yield of usually only 6%-8%, far from meeting the actual application requirements, which has become a key bottleneck restricting its promotion.

[0003] Sludge anaerobic fermentation mainly includes four stages of hydrolysis, acidification, hydrogen production, and methane production, among which hydrolysis is the rate-limiting step. Due to the dense structure of cell walls and extracellular polymeric substances (EPS) in excess sludge, the release of organic matter is severely hindered, limiting the generation efficiency of short-chain fatty acids (SCFAs). To improve the hydrolysis and acidification effect, there are mainly three types of existing strengthening methods: physical methods such as ultrasonic, thermal hydrolysis, and microwave treatment, which can improve the hydrolysis efficiency but have high energy consumption and large equipment investment, making it difficult to be applied on a large scale. Biological methods by adding specific enzyme preparations or functional microorganisms can improve digestion performance, but are limited by cost and strain domestication, and are hindered in promotion. Chemical methods such as alkaline pretreatment, surfactants, and oxidizing agents can significantly improve the acid production efficiency, but there are environmental risks and cost problems.

[0004] In summary, the existing methods have deficiencies in efficiency, cost and environmental friendliness, and it is urgent to develop more efficient, economical and green strengthening technologies. SUMMARY

[0005] In view of the low hydrolysis efficiency and low SCFAs yield in the existing residual sludge anaerobic fermentation acid production technology, the present application provides a method for producing short-chain fatty acids (SCFAs) based on sulfate synergistic electron transfer to strengthen sludge anaerobic fermentation. The method uses sulfate (SO4 2- ) to optimize the electron transfer path, significantly strengthen the sludge hydrolysis and acid production process, and ultimately achieve efficient resource conversion of residual sludge, providing a green and economical new approach for sludge treatment.

[0006] To achieve the above-mentioned application purposes, the technical scheme adopted by the present application is: a method for producing fatty acids based on sulfate synergistic electron transfer to strengthen sludge anaerobic fermentation, the method comprising the following steps: placing residual sludge and inoculated sludge in an anaerobic fermentation device, stirring and mixing uniformly, and then adjusting the initial pH value; then adding a sulfate solution, and continuing to stir and mix uniformly at 20-25°C; then removing oxygen in the anaerobic fermentation device with nitrogen, and sealing the anaerobic fermentation device; and performing anaerobic fermentation in a constant-temperature shaker.

[0007] Further, the fatty acids are short-chain fatty acids.

[0008] Further, the short-chain fatty acids include acetic acid, propionic acid, n-butyric acid, iso-butyric acid, n-valeric acid and / or iso-valeric acid.

[0009] Further, the residual sludge is taken from the return sludge of the secondary sedimentation tank of a sewage treatment plant, and the sludge concentration is 6.0-7.0g / L in terms of volatile suspended solids (VSS).

[0010] Further, the inoculated sludge is taken from the anaerobic section sludge of a sewage treatment plant using the anaerobic-anoxic-aerobic (AAO) process, and is concentrated by natural sedimentation, and the sludge concentration is 3.5-5.0g / L in terms of volatile suspended solids (VSS).

[0011] Further, the residual sludge: inoculated sludge = (20-30) : (60-70) by volume ratio.

[0012] Further, the initial pH value is adjusted to 9-10.

[0013] Further, the sulfate is Na2SO4, K2SO4 or MgSO4. Preferably, Na2SO4.

[0014] Further, the sulfate solution is added so that the concentration of SO4 2- is 3000-6000mg / L.

[0015] Further, the anaerobic fermentation is carried out in a constant temperature shaker, and specifically, the temperature is controlled to be 35±1 DEG C, the oscillation speed is 120rpm-150rpm, and the anaerobic fermentation time is 5-14 days.

[0016] Compared with the prior art, the present application has the following advantages:

[0017] 1. The sludge anaerobic fermentation treatment method provided by the present application adds sulfate before fermentation, which improves the Zeta potential of the residual sludge suspension and destroys the stable structure of the sludge floc. At the same time, the sulfate can penetrate into the sludge cells, cause cell lysis and release intracellular organic matter, provide more organic matter for sludge acid production fermentation, and create favorable conditions for SCFA production.

[0018] 2. The sludge anaerobic fermentation treatment method provided by the present application promotes sludge reduction and resource utilization, and realizes resource recycling and utilization of organic matter in sludge. The generated SCFAs can replace traditional carbon sources (such as sodium acetate) for denitrification and phosphorus removal in sewage plants or as a bio-refining raw material, and have good economic value.

[0019] 3. The sludge anaerobic fermentation treatment method provided by the present application uses sodium sulfate (Na2SO4) as the core additive, which is widely available, low in price, suitable in reactivity, and low in environmental risk. The method introduces sulfate on the basis of conventional alkaline fermentation, which is simple to operate and does not require complex equipment or high-energy consumption treatment units (such as ultrasonic, thermal hydrolysis). Compared with methods that require the addition of surfactants, oxidants or expensive enzyme preparations, the present application significantly reduces the treatment cost and the potential risk of secondary pollution. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is a graph of the accumulation amount of short-chain fatty acids during anaerobic fermentation in the examples and comparative examples of the present application.

[0021] Figure 2 is a graph of the proportion of short-chain fatty acid components during anaerobic fermentation in the examples and comparative examples of the present application. DETAILED DESCRIPTION

[0022] The embodiments of the present application will be described in detail below with reference to the accompanying drawings. The present embodiment is based on the technical scheme of the present application, and provides detailed implementation methods and specific operation procedures. The embodiments described in the present application are only a part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of the present application.

[0023] In the parts of the embodiments where specific conditions are not explicitly labeled, they are operated according to the conventional conditions or the conditions recommended by the manufacturer. If the reagents or instruments used are not specified by the manufacturer, they are all conventional products that can be purchased through market channels.

[0024] Example 1: Method for enhancing sludge anaerobic fermentation to produce short-chain fatty acids based on sulfate synergistic electron transfer

[0025] The method comprises the following steps:

[0026] Residual sludge: The backflow sludge taken from the secondary sedimentation tank of a municipal wastewater treatment plant in Shenyang has a sludge concentration of 6.1 g / L in terms of volatile suspended solids (VSS).

[0027] Inoculated sludge: The sludge taken from the anaerobic section of an AAO process wastewater treatment plant in Shenyang is concentrated by natural sedimentation, and has a sludge concentration of 3.5 g / L in terms of volatile suspended solids (VSS).

[0028] 1. Put 20 mL of the residual sludge filtered and 68 mL of the inoculated sludge mixed uniformly into an anaerobic fermentation bottle with an effective volume of 100 mL.

[0029] 2. Add NaOH solution with a concentration of 1 mol / L to the mixed sludge to adjust the initial pH value of the system to 10.0.

[0030] 3. Add Na2SO4 solution to make the concentration of SO4 2- 6000 mg / L, and continue to stir to ensure thorough mixing at 20-25°C.

[0031] 4. Continuously introduce high-purity nitrogen into the anaerobic fermentation bottle for 10-20 min to completely remove the oxygen in the anaerobic fermentation bottle and create a strict anaerobic environment, and then immediately seal the bottle mouth with a rubber plug.

[0032] 5. Put the sealed anaerobic fermentation bottle into a constant-temperature shaker, set the temperature to 35±1°C, and start the anaerobic fermentation for 14 days at a shaking speed of 130 rpm.

[0033] 6. Take samples regularly during the fermentation process to monitor the changes in SCFAs concentration.

[0034] When the fermentation is carried out for 7 days, the cumulative yield of SCFAs reaches a peak value. Among them, the yield of acetic acid is the highest, and the results are shown in Table 1.

[0035] Example 2: Method for enhancing sludge anaerobic fermentation to produce short-chain fatty acids based on sulfate synergistic electron transfer

[0036] The method comprises the following steps:

[0037] Excess sludge: The return sludge from the secondary sedimentation tank of a municipal wastewater treatment plant in Shenyang, with a concentration of 6.1 g / L in terms of volatile suspended solids (VSS).

[0038] Inoculum sludge: The anaerobic sludge from an AAO process wastewater treatment plant in Shenyang, concentrated by natural sedimentation, with a concentration of 3.5 g / L in terms of volatile suspended solids (VSS).

[0039] 1. Put 20 mL of excess sludge filtered and 68 mL of inoculum sludge mixed uniformly into an anaerobic fermentation bottle with an effective volume of 100 mL.

[0040] 2. Add NaOH solution with a concentration of 1 mol / L to adjust the initial pH of the system to 10.0.

[0041] 3. Add Na2SO4 solution to make the concentration of SO4 2- 4500 mg / L, and continue stirring to ensure thorough mixing at 20-25°C.

[0042] 4. Continuously introduce high-purity nitrogen into the anaerobic fermentation bottle for 10-20 min to completely remove the oxygen in the anaerobic fermentation bottle and create a strict anaerobic environment, then immediately seal the bottle mouth with a rubber plug.

[0043] 5. Place the sealed anaerobic fermentation bottle in a constant temperature shaker, set the temperature to 35±1°C, and start the anaerobic fermentation at a shaking speed of 130 rpm for 14 days.

[0044] 6. Take samples regularly during the fermentation process to monitor the changes in SCFAs concentration.

[0045] The cumulative SCFAs production reached a peak at the 7th day of fermentation, with the highest production of acetic acid. The results are shown in Table 1.

[0046] Example 3: Method for enhancing sludge anaerobic fermentation to produce short-chain fatty acids based on sulfate salt and electron transfer

[0047] The method includes the following steps:

[0048] Excess sludge: The return sludge from the secondary sedimentation tank of a municipal wastewater treatment plant in Shenyang, with a concentration of 6.1 g / L in terms of volatile suspended solids (VSS).

[0049] Inoculum sludge: The anaerobic sludge from an AAO process wastewater treatment plant in Shenyang, concentrated by natural sedimentation, with a concentration of 3.5 g / L in terms of volatile suspended solids (VSS).

[0050] 1. Put 20 mL of the screened excess sludge and 68 mL of the filtered and mixed inoculation sludge into an anaerobic fermentation bottle with an effective volume of 100 mL, and mix them evenly under stirring.

[0051] 2. Add NaOH solution with a concentration of 1 mol / L to the mixed sludge to adjust the initial pH value of the system to 10.0.

[0052] 3. Add Na2SO4 solution to make the concentration of SO4 2- be 3000 mg / L, and continue stirring to ensure sufficient mixing at 20-25°C.

[0053] 4. Continuously introduce high-purity nitrogen into the anaerobic fermentation bottle for 10-20 min to completely remove oxygen in the anaerobic fermentation bottle and create a strict anaerobic environment, and then immediately seal the bottle mouth with a rubber plug.

[0054] 5. Put the sealed anaerobic fermentation bottle into a constant-temperature shaker, set the temperature to 35±1°C, and start the anaerobic fermentation at a shaking speed of 130 rpm for 14 days.

[0055] 6. Take samples regularly during the fermentation to monitor the changes in SCFAs concentration.

[0056] When the fermentation is carried out to the 7th day, the cumulative yield of SCFAs reaches a peak value. Among them, the yield of acetic acid is the highest, and the results are shown in Table 1.

[0057] Example 4 Method for producing short-chain fatty acids by anaerobic fermentation of sludge based on sulfate salt and electron transfer enhancement

[0058] The method comprises the following steps:

[0059] Excess sludge: taken from the return sludge of the secondary sedimentation tank of a municipal wastewater treatment plant in Shenyang, the sludge concentration is 6.9 g / L in terms of volatile suspended solids (VSS).

[0060] Inoculation sludge: taken from the anaerobic section sludge of an AAO process wastewater treatment plant in Shenyang, and concentrated by natural sedimentation, the sludge concentration is 4.5 g / L in terms of volatile suspended solids (VSS).

[0061] 1. Put 26 mL of the screened excess sludge and 62 mL of the filtered and mixed inoculation sludge into an anaerobic fermentation bottle with an effective volume of 100 mL, and mix them evenly under stirring.

[0062] 2. Add NaOH solution with a concentration of 1 mol / L to the mixed sludge to adjust the initial pH value of the system to 9.

[0063] 3. Add Na2SO4 solution to make the concentration of SO4 2-The concentration of Na2SO4 is 3800 mg / L, and the stirring is continued at 20-25°C to ensure thorough mixing.

[0064] 4. Continue to pass high-purity nitrogen into the anaerobic fermentation bottle for 10-20 min to completely remove the oxygen in the anaerobic fermentation bottle and create a strict anaerobic environment, and then immediately seal the bottle mouth with a rubber plug.

[0065] 5. Place the sealed anaerobic fermentation bottle in a constant temperature shaker, set the temperature to 35±1°C, and start the anaerobic fermentation for 14 days at a shaking speed of 130 rpm.

[0066] 6. Take samples regularly during the fermentation process to monitor the changes in SCFA concentration.

[0067] When the fermentation is carried out for 5 days, the cumulative yield of SCFAs reaches a peak. Among them, the yield of acetic acid is the highest, and the results are shown in Table 1.

[0068] Example 5 Method for enhancing anaerobic fermentation of sludge to produce short-chain fatty acids based on sulfate synergistic electron transfer

[0069] The method comprises the following steps:

[0070] Residual sludge: taken from the return sludge of the secondary sedimentation tank of a municipal wastewater treatment plant in Shenyang, the concentration of the sludge is 6.9 g / L in terms of volatile suspended solids (VSS).

[0071] Inoculated sludge: taken from the anaerobic section sludge of a wastewater treatment plant using AAO process in Shenyang, and concentrated by natural sedimentation, the concentration of the sludge is 4.5 g / L in terms of volatile suspended solids (VSS).

[0072] 1. Put 26 mL of the screened residual sludge and 62 mL of the filtered and mixed inoculated sludge into an anaerobic fermentation bottle with an effective volume of 100 mL, and mix them evenly under stirring.

[0073] 2. Add NaOH solution with a concentration of 1 mol / L to the mixed sludge to adjust the initial pH value of the system to 10.

[0074] 3. Add Na2SO4 solution to make the concentration of SO4 2- The concentration of Na2SO4 is 3800 mg / L, and the stirring is continued at 20-25°C to ensure thorough mixing.

[0075] 4. Continue to pass high-purity nitrogen into the anaerobic fermentation bottle for 10-20 min to completely remove the oxygen in the anaerobic fermentation bottle and create a strict anaerobic environment, and then immediately seal the bottle mouth with a rubber plug.

[0076] 5. Place the sealed anaerobic fermentation bottle in a constant temperature shaker, set the temperature to 35±1°C, and start the anaerobic fermentation for 14 days at a shaking speed of 130 rpm.

[0077] 6. Regularly sampling during the fermentation process to monitor the SCFAs concentration change.

[0078] When the fermentation proceeds to the 9th day, the SCFAs cumulative production reaches the peak value. Among them, the acetic acid production is the highest, and the results are shown in Table 1.

[0079] Comparative Example 1

[0080] The method comprises the following steps:

[0081] Residual sludge: the backflow sludge taken from the secondary sedimentation tank of a municipal wastewater treatment plant in Shenyang, with a sludge concentration of 6.1 g / L in terms of volatile suspended solids (VSS).

[0082] Inoculated sludge: the sludge taken from the anaerobic section of a wastewater treatment plant using AAO process in Shenyang, and concentrated by natural sedimentation, with a sludge concentration of 3.5 g / L in terms of volatile suspended solids (VSS).

[0083] 1. Put 20 mL of the screened residual sludge and 68 mL of the mixed and uniformly filtered inoculated sludge into an anaerobic fermentation bottle with an effective volume of 100 mL, and mix them uniformly under stirring.

[0084] 2. Add NaOH solution with a concentration of 1 mol / L to the mixed sludge to adjust the initial pH value of the system to 10.

[0085] 3. Continuously introduce high-purity nitrogen into the anaerobic fermentation bottle for 10-20 min to completely remove the oxygen in the anaerobic fermentation bottle and create a strict anaerobic environment, and then immediately seal the bottle mouth with a rubber plug.

[0086] 4. Put the sealed anaerobic fermentation bottle into a constant temperature shaker, set the temperature to 35±1℃, and set the shaking speed to 130 rpm, and start the anaerobic fermentation for 14 days.

[0087] 5. Regularly sampling during the fermentation process to monitor the SCFAs concentration.

[0088] When the fermentation proceeds to the 7th day, the SCFAs cumulative production reaches the peak value. Among them, the acetic acid production is the highest, and the results are shown in Table 1.

[0089] Table 1

[0090]

[0091]

[0092] As can be seen from Table 1, the change of the amount of sulfate salt and the initial conditions of the system in the method for producing acid by anaerobic fermentation of sludge with sulfate salt and electron transfer enhancement is tested. In Examples 1-3, under the same initial residual sludge volume and pH conditions, as the amount of sodium sulfate increases, the cumulative SCFAs yield also gradually increases, especially when the amount of sodium sulfate is 6000 mg / L, the cumulative SCFAs yield reaches a peak of 3316 mg / L g VSS at the 7th day of fermentation, which is 1.7 times the cumulative SCFAs yield in the comparative example without adding sulfate salt. In addition, in Examples 1-3 and Example 5, under the same initial pH conditions, the increase of the initial volume of residual sludge can increase the cumulative SCFAs. In addition, compared with Comparative Example 4 and Example 5, as the pH value increases from 9 to 10, the cumulative SCFAs concentration also increases accordingly, and the increase of the cumulative SCFAs yield in Example 5 compared with Comparative Example 1 is 3.25 times.

[0093] Figure 1 The cumulative yield diagram of Examples 1-5 and Comparative Example 1 during anaerobic fermentation is given in Table 1, and the total cumulative SCFAs yield is calculated, wherein the total cumulative SCFAs yield of Example 5 is the highest, which is 4.25 times that of Comparative Example 1.

[0094] Figure 2 It is shown that the proportion of SCFAs acetic acid in Examples 1-5 is significantly higher than that in Comparative Example 1, because the present application uses sulfate salt to mediate the change of the electron transfer path in the organic matter degradation process, and the sulfate reducing bacteria (SRB) uses SO4 2- as an electron acceptor, and improves the efficiency of organic matter oxidation to acetic acid through sulfur-mediated electron transfer, thereby enhancing the SCFAs yield.

[0095] The detailed description of the examples in the specification is intended to help the practitioners in the technical field to understand and apply the present application. Based on the content herein, the skilled person in the relevant field can conveniently make adaptive adjustments to the described examples without making creative contributions, and extend the core principles described to other application scenarios, such as other organic solid waste besides residual sludge. Therefore, the legal protection scope of the present application not only covers the above specific examples. Any optimization scheme and adaptive change implemented by a person skilled in the art based on the disclosure of the present application without deviating from the core idea of the present application falls within the scope of the claims of the present application.

Claims

1. A method for enhancing production of fatty acids from anaerobic fermentation of sludge based on sulfate salt cooperation electron transfer, characterized in that, The method comprises the following steps: placing residual sludge and inoculated sludge in an anaerobic fermentation device, stirring and mixing uniformly, adjusting the initial pH value, then adding a sulfate solution, continuously stirring and mixing uniformly at 20-25 DEG C, then driving out oxygen in the anaerobic fermentation device with nitrogen, sealing the anaerobic fermentation device, and performing anaerobic fermentation in a constant-temperature shaking bed.

2. The method for enhancing the production of fatty acids from anaerobic fermentation of sludge based on sulfate salt and electron transfer according to claim 1, characterized in that, The fatty acid is a short-chain fatty acid.

3. The method according to claim 2, wherein the method is characterized by, The short-chain fatty acid includes acetic acid, propionic acid, n-butyric acid, iso-butyric acid, n-valeric acid and / or iso-valeric acid.

4. The method for enhancing production of fatty acids from anaerobic fermentation of sludge based on sulfate salt synergistic electron transfer according to claim 1, 2 or 3, characterized in that, The residual sludge is taken from the backflow sludge of a secondary sedimentation tank of a sewage treatment plant, and the sludge concentration is 6.0-7.0 g / L in terms of volatile suspended solids (VSS).

5. The method for enhancing the production of fatty acids from anaerobic fermentation of sludge based on sulfate salt synergistic electron transfer according to claim 1, 2 or 3, characterized in that, The inoculated sludge is taken from the sludge of an anaerobic section of a sewage treatment plant adopting an anaerobic-anoxic-aerobic process, and is concentrated by natural sedimentation, and the sludge concentration is 3.5-5.0 g / L in terms of volatile suspended solids (VSS).

6. The method for enhancing the production of fatty acids from anaerobic fermentation of sludge based on sulfate salt synergistic electron transfer according to claim 1, 2 or 3, characterized in that, The residual sludge and the inoculated sludge are in a volume ratio of (20-30):(60-70).

7. The method for enhancing the production of fatty acids from anaerobic fermentation of sludge based on sulfate salts and synergistic electron transfer according to claim 1, 2 or 3, characterized in that, The initial pH value is adjusted to 9-10.

8. The method for enhancing the production of fatty acids from anaerobic fermentation of sludge based on sulfate salt synergistic electron transfer according to claim 1, 2 or 3, characterized in that, The sulfate is Na2SO4, K2SO4 or MgSO4.

9. The method according to claim 8, wherein the method is characterized by, Sulphate solution was added to make SO4 2- concentration 3000 mg / L - 6000 mg / L.

10. The method for enhancing the production of fatty acids from anaerobic fermentation of sludge based on sulfate salt synergistic electron transfer according to claim 1, 2 or 3, characterized in that, The anaerobic fermentation in the constant-temperature shaking bed is specifically performed by controlling the temperature to be 35±1 DEG C, the oscillation speed to be 120-150 rpm, and the anaerobic fermentation time to be 5-14 days.

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