Method for producing acid by co-fermentation of sulfur reduction reinforced waste oil and excess sludge

Abstract

The invention relates to a method for producing acid through co-fermentation of sulfur reduction reinforced waste oil and excess sludge. Comprising the following steps: 1) treating residual sludge, standing for a period of time, and removing part of supernate to obtain treated residual sludge; (2) putting the residual sludge treated in the step (1) into a reaction device, and then adding waste oil; (3) adding sulfide into the reaction device; and 4) fermenting in an anaerobic environment. According to the present invention, the sulfur substance is added as the electron acceptor, such that the LCFA degradation can be effectively promoted, the sulfur substance can effectively promote the acid production under the alkaline condition, and the incompletely oxidized sulfate reducing bacteria (SRB) is successfully enriched so as to alleviate the LCFA inhibition effect and significantly improve the acid production efficiency;

Description

Technical Field

[0001] The present invention relates to the technical field of waste grease treatment, and particularly relates to a method for enhancing the co-fermentation of waste grease and excess sludge to produce acid by sulfur reduction. Background Art

[0002] Grease waste refers to inedible animal and vegetable oils and fats generated by industries such as the food processing industry and the catering industry, mainly including: (1) inferior or expired subcutaneous fat, internal organs and other scraps generated during meat processing; (2) animal oils and fats generated after the treatment of dead and diseased livestock and poultry; (3) fried waste oil in the catering industry and grease waste generated after separation by an oil-water separator, etc. With the continuous improvement of the economic level, the consumption of edible oils and animal meat products in China has been increasing year by year, and the generated grease waste is also increasing.

[0003] Improper or untimely treatment of grease may lead to serious environmental pollution, including water body and soil pollution, which in turn affects the ecological balance and plant growth. In addition, such improper treatment may pose a threat to public health, such as health risks of causing skin diseases and respiratory problems. The accumulation of grease in the drainage system easily leads to pipeline blockage, thereby increasing the maintenance and cleaning costs and may damage the normal operation of industrial equipment, resulting in mechanical failures.

[0004] Currently, among the domestic resource treatment methods for waste grease, anaerobic fermentation technology is a commonly used treatment method, generating short-chain fatty acids (VFA) and methane through anaerobic fermentation. Anaerobic fermentation technology refers to the process of stabilizing organic waste by the metabolic activities of microorganisms in an anaerobic environment, which has the advantages of mild reaction conditions, low energy consumption, and the ability to generate high-value-added intermediate product VFA. Using anaerobic fermentation technology to efficiently convert waste grease into small molecule organic acids (VFA) has broad development prospects. However, using waste grease as a single substrate for anaerobic fermentation will lead to nutritional imbalance. Therefore, mixing and using waste biomass rich in nutrients such as nitrogen and phosphorus has become an important development trend. Excess sludge, as the main by-product of urban sewage treatment, is rich in nitrogen and phosphorus elements. Co-fermentation with grease can not only introduce hydrolysis and acidification bacteria groups, but also adjust the substrate composition, thereby providing balanced nutrition for anaerobic bacteria groups.

[0005] The anaerobic fermentation treatment of waste grease and excess sludge has gradually become a research hotspot, attracting the attention of many researchers. The research in this field not only involves the resource utilization of waste, but also relates to environmental protection and sustainable development. However, the degradation efficiency of organic matter in the existing anaerobic fermentation process of waste grease and excess sludge is not high, and the acid production rate is low. Summary of the Invention

[0006] The object of the present invention is to provide a method for enhancing the co-fermentation of waste grease and excess sludge to produce acid by sulfur reduction, so as to solve the problems of low organic matter degradation efficiency and low acid production rate existing in the prior art.

[0007] To achieve the above object, a method for enhancing the co-fermentation of waste grease and excess sludge to produce acid by sulfur reduction according to the present invention adopts the following technical solution: A method for enhancing the co-fermentation of waste grease and excess sludge to produce acid by sulfur reduction, comprising the following steps:

[0008] 1) Treat the excess sludge, then let it stand for a period of time, remove part of the supernatant to obtain the treated excess sludge;

[0009] 2) Put the treated excess sludge in step 1) into a reaction device, and then add waste grease;

[0010] 3) Add sulfide to the reaction device;

[0011] 4) Conduct fermentation under anaerobic conditions.

[0012] In step 1), the TS concentration in the treated excess sludge is 18000 - 20000 mg / L.

[0013] In step 2), the ratio of waste grease to sludge is 0.51 g / gTS.

[0014] In step 3), the sulfide is at least one of sodium sulfate, sodium sulfite, sodium thiosulfate and sulfur.

[0015] Control the sulfur dosing concentration to be 1200 mgS / L.

[0016] In step 4), introduce nitrogen gas into the reaction device to create an anaerobic environment, and the introduction amount of nitrogen gas is 2.5 times the volume of the reaction device.

[0017] In step 1), the treatment method for the excess sludge is: wash and filter the excess sludge to remove large particle impurities.

[0018] In step 4), the reaction temperature is 35 °C and the pH value is 9 ± 0.5.

[0019] In step 4), a stirring mechanism is provided in the reaction device, and the rotation speed is 400 ± 550 rpm.

[0020] In step 4), the reaction process is in a light-proof environment.

[0021] Advantages of the present invention: Adding sulfur substances as electron acceptors can effectively promote the degradation of LCFA, and sulfur substances can effectively promote acid production under alkaline conditions, and incompletely oxidized sulfate-reducing bacteria (SRB) are successfully enriched, thereby alleviating the inhibitory effect of LCFA and significantly improving the acid production efficiency. Brief Description of the Drawings

[0022] Figure 1 It shows the fatty acid conversion of Experimental Examples 1 to 5 and Comparative Examples of the present invention;

[0023] Figure 2 It shows the acid production rate and acidification rate of Experimental Examples 1 to 5 and Comparative Examples of the present invention during the fermentation cycle;

[0024] Figure 3 It shows the degradation rate of LCFA of Experimental Examples 1 to 5 and Comparative Examples of the present invention during the fermentation cycle. Detailed Embodiments

[0025] Experimental Example 1

[0026] 1) Treat the excess sludge, then let it stand for a period of time, and remove part of the supernatant to obtain the treated excess sludge.

[0027] Specifically, in this step, the excess sludge is washed and filtered through a 65-mesh sieve to remove large particle impurities, then let it stand for a period of time, and remove part of the supernatant. The TS concentration in the treated excess sludge is 19000 mg / L.

[0028] 2) Put the treated excess sludge in step 1) into the reaction device, and then add waste grease.

[0029] In this step, a stirring mechanism is provided in the reaction device, and the ratio of waste grease to sludge is 0.51 g / gTS, and C / N = 100:5 is controlled.

[0030] 3) Add sulfide to the reaction device.

[0031] Sodium sulfate is used as the sulfide. The dosing concentration of sulfur is controlled at 1200 mgS / L.

[0032] 4) Ferment in an anaerobic environment.

[0033] In this step, nitrogen is introduced into the reaction device to create an anaerobic environment. The introduction amount of nitrogen is 2.5 times the volume of the reaction device. The reaction temperature is 35 °C, and the pH value is 9 ± 0.5. The rotation speed is 400 ± 550 rpm. The reaction process is in a light-shielded environment.

[0034] This experimental example is denoted as R2-Na2SO4.

[0035] Experimental Example 2

[0036] 1) Treat the excess sludge, then let it stand for a period of time to remove part of the supernatant, obtaining the treated excess sludge.

[0037] Specifically, in this step, the excess sludge is washed and filtered through a 65-mesh sieve to remove large particle impurities, then let it stand for a period of time to remove part of the supernatant, and the TS concentration in the treated excess sludge is 19000 mg / L.

[0038] 2) Put the treated excess sludge in step 1) into the reaction device, and then add waste grease.

[0039] In this step, a stirring mechanism is provided in the reaction device, and the ratio of waste grease to sludge is 0.51 g / gTS, controlling C / N = 100:5.

[0040] 3) Add sulfide to the reaction device.

[0041] Sodium sulfite is used as the sulfide. Control the dosing concentration of sulfur to be 1200 mgS / L.

[0042] 4) Ferment under an anaerobic environment.

[0043] In this step, nitrogen is introduced into the reaction device to create an anaerobic environment. The introduction amount of nitrogen is 2.5 times the volume of the reaction device. The reaction temperature is 35 °C, the pH value is 9 ± 0.5. The rotation speed is 400 ± 550 rpm. The reaction process is in a light-shielded environment.

[0044] This experimental example is denoted as R3-Na2SO3.

[0045] Experimental Example Three

[0046] 1) Treat the excess sludge, then let it stand for a period of time to remove part of the supernatant, obtaining the treated excess sludge.

[0047] Specifically, in this step, the excess sludge is washed and filtered through a 65-mesh sieve to remove large particle impurities, then let it stand for a period of time to remove part of the supernatant, and the TS concentration in the treated excess sludge is 19000 mg / L.

[0048] 2) Put the treated excess sludge in step 1) into the reaction device, and then add waste grease.

[0049] In this step, a stirring mechanism is provided in the reaction device, and the ratio of waste grease to sludge is 0.51 g / gTS, controlling C / N = 100:5.

[0050] 3) Add sulfide to the reaction device.

[0051] Sulfide is sodium thiosulfate. The dosing concentration of sulfur is controlled at 1200 mgS / L.

[0052] 4) Fermentation is carried out under anaerobic conditions.

[0053] In this step, nitrogen is introduced into the reaction device to create an anaerobic environment. The amount of nitrogen introduced is 2.5 times the volume of the reaction device. The reaction temperature is 35 °C, the pH value is 9 ± 0.5, and the rotation speed is 400 ± 550 rpm. The reaction process is in a light-shielded environment.

[0054] This experimental example is denoted as R4-Na2S2O3.

[0055] Experimental Example Four

[0056] 1) Treat the excess sludge, then let it stand for a period of time to remove part of the supernatant to obtain the treated excess sludge.

[0057] Specifically, in this step, the excess sludge is washed and filtered through a 65-mesh sieve to remove large particle impurities, then let it stand for a period of time to remove part of the supernatant. The TS concentration in the treated excess sludge is 19000 mg / L.

[0058] 2) Put the treated excess sludge from step 1) into the reaction device, and then add waste grease.

[0059] In this step, a stirring mechanism is provided in the reaction device, and the ratio of waste grease to sludge is 0.51 g / gTS, and C / N is controlled at 100:5.

[0060] 3) Add sulfide to the reaction device.

[0061] The sulfide is elemental sulfur. The dosing concentration of sulfur is controlled at 1200 mgS / L.

[0062] 4) Fermentation is carried out under anaerobic conditions.

[0063] In this step, nitrogen is introduced into the reaction device to create an anaerobic environment. The amount of nitrogen introduced is 2.5 times the volume of the reaction device. The reaction temperature is 35 °C, the pH value is 9 ± 0.5, and the rotation speed is 400 ± 550 rpm. The reaction process is in a light-shielded environment.

[0064] This experimental example is denoted as R5-S.

[0065] Experimental Example Five

[0066] 1) Treat the excess sludge, then let it stand for a period of time to remove part of the supernatant to obtain the treated excess sludge.

[0067] Specifically, in this step, the excess sludge is washed and filtered through a 65-mesh sieve to remove large particulate impurities, and then left standing for a period of time to remove part of the supernatant. The TS concentration in the treated excess sludge is 18,000 mg / L.

[0068] 2) Put the treated excess sludge from step 1) into a reaction device, and then add waste grease.

[0069] In this step, a stirring mechanism is provided in the reaction device, and the ratio of waste grease to sludge is 0.51 g / gTS, controlling C / N = 100:5.

[0070] 3) Add sulfide to the reaction device.

[0071] Sodium sulfate is used as the sulfide. Control the dosing concentration of sulfur to be 1,200 mgS / L.

[0072] 4) Ferment under an anaerobic environment.

[0073] In this step, nitrogen is introduced into the reaction device to create an anaerobic environment. The introduction amount of nitrogen is 2.5 times the volume of the reaction device. The reaction temperature is 35 °C, the pH value is 9 ± 0.5. The rotation speed is 400 ± 550 rpm. The reaction process is in a light-shielded environment.

[0074] Experimental Example Six

[0075] 1) Treat the excess sludge, and then leave it standing for a period of time to remove part of the supernatant to obtain the treated excess sludge.

[0076] Specifically, in this step, the excess sludge is washed and filtered through a 65-mesh sieve to remove large particulate impurities, and then left standing for a period of time to remove part of the supernatant. The TS concentration in the treated excess sludge is 20,000 mg / L.

[0077] 2) Put the treated excess sludge from step 1) into a reaction device, and then add waste grease.

[0078] In this step, a stirring mechanism is provided in the reaction device, and the ratio of waste grease to sludge is 0.51 g / gTS, controlling C / N = 100:5.

[0079] 3) Add sulfide to the reaction device.

[0080] Sodium sulfate is used as the sulfide. Control the dosing concentration of sulfur to be 1,200 mgS / L.

[0081] 4) Ferment under an anaerobic environment.

[0082] In this step, nitrogen gas is introduced into the reaction device to create an anaerobic environment. The amount of nitrogen gas introduced is 2.5 times the volume of the reaction device. The reaction temperature is 35 °C, and the pH value is 9 ± 0.5. The rotation speed is 400 ± 550 rpm. The reaction process is in a light-shielded environment.

[0083] Control example

[0084] The difference from Experimental Example 1 is only that no sulfur substance is added. This control example is denoted as R1 - blank.

[0085] The parameters of R1 - blank, R2 - Na2SO4, R3 - Na2SO3, R4 - Na2S2O3, and R5 - S are shown in the following table:

[0086]

[0087] The results after the reaction are as follows:

[0088] As Figure 1 shown, a) is volatile fatty acid, and b) is long-chain fatty acid. In the study of co-fermentation of grease and excess sludge to produce acid, the content changes of volatile fatty acids and long-chain fatty acids are important indicators for evaluating fermentation efficiency. From Figure 1 (a) and (b), it can be seen that VFA is continuously generated while LCFA is continuously decreasing, and finally both tend to be stable. However, different treatment conditions have a significant impact on the yields of total volatile fatty acids and total long-chain fatty acids, and the order of influence is R2 (sodium sulfate) > R3 (sodium sulfite) > R4 (sodium thiosulfate) > R5 (sulfur) > R1 (blank).

[0089] It can be seen that the addition of sulfur-containing substances in high valence states significantly promotes the production of VFA and the degradation of LCFA, and sodium sulfate has the most significant effect. This result suggests that in the anaerobic fermentation process, selecting a suitable sulfur-containing electron acceptor can effectively improve the degradation efficiency of organic matter and thus optimize the process of fermentation to produce acid.

[0090] Regarding the acid production rate and acidification rate during the fermentation cycle, as Figure 2 shown. The anaerobic fermentation performance is evaluated using the acidification rate and acid production rate. Among them, the acidification rate focuses on the conversion efficiency of soluble chemical oxygen demand (SCOD), while the acid production rate pays more attention to the rate of organic matter generating VFA during the anaerobic fermentation process. By combining these two indicators, the metabolic activities of microorganisms in anaerobic fermentation can be better understood, the fermentation conditions can be optimized, and the conversion efficiency of organic matter and the acid production ability can be improved. It can be seen from Figure 2 that different treatment conditions have a significant impact on the yields of total volatile fatty acids (TVFA) and total long-chain fatty acids (TLCFA) and their acidification rates.

[0091] The addition of high-valent sulfur-containing substances has a significant effect on the production and decline of volatile fatty acids and long-chain fatty acids. Under the treatment conditions of sodium sulfate (R2) and sodium sulfite (R3), the concentrations of VFA and LCFA both rose or fell rapidly in the early stage, fluctuated steadily after reaching the peak, and both had higher acid yields and acidification rates, which were about 2 times that of the blank control group, indicating that these two systems can effectively promote the conversion of organic components in the system to VFA, and oils and fats as carbon sources can be well synergistically fermented with residual sludge, relieving the inhibitory effect of LCFA and improving the metabolism of oils and fats and the fermentation acid production efficiency of residual sludge.

[0092] like Figure 3 As shown in Figure 2, this study revealed the differential regulatory effects of different sulfur-based electron acceptors on the degradation of long-chain fatty acids (LCFA) under alkaline conditions (pH = 9) ( Figure 3 ). It shows that the addition of sodium sulfate (R2-Na2SO4) increased the LCFA degradation rate to 44.75%, which is 6.8 times higher than that of the blank group (R1), which is closely related to the mechanism of sulfate strengthening the β-oxidation pathway and the activity of the electron transport chain. Similarly, the study of the Fe1-xNixS / sulfite system showed that non-radical pathways (such as direct electron transfer) in an alkaline environment can significantly improve the degradation efficiency of pollutants, which is consistent with the hypothesis that sulfate may accelerate electron transfer through similar pathways in this study. The degradation rate of 29.68% in the sodium sulfite (R3-Na2SO3) group suggests that although the sulfur oxidation state (+4 valence) can participate in redox reactions, its electron acceptance ability may be weaker than the efficient electron transfer characteristics of sulfate (+6 valence). It is worth noting that the sodium thiosulfate (R4-Na2S2O3) and elemental sulfur (R5-S) groups were not significantly different from the blank group, which may be related to the chemical stability of sulfur forms and microbial metabolic preferences. Studies have found that elemental sulfur plays a role in the biosulfur production process mainly through the sulfur reduction process mediated by microorganisms. However, in this study, elemental sulfur lacks an effective activation mechanism, which makes it unable to effectively participate in the β-oxidation cycle of LCFA. In addition, sodium thiosulfate may undergo disproportionation reaction under alkaline conditions to generate S 2- and SO3 2- , these intermediates may inhibit the activity of key enzymes or compete with LCFAs for electron acceptors.

Claims

1. A method for enhancing the co-fermentation of waste grease and excess sludge to produce acids by sulfur reduction, characterized in that, It includes the following steps: 1) Treat the excess sludge, then let it stand for a period of time, remove part of the supernatant to obtain the treated excess sludge; 2) Put the treated excess sludge in step 1) into a reaction device, and then add waste grease; 3) Add sulfide to the reaction device; 4) Ferment in an anaerobic environment.

2. The method for enhancing the co-fermentation of waste grease and excess sludge to produce acid by sulfur reduction according to claim 1, wherein: In step 1), the TS concentration in the treated excess sludge is 18000 - 20000 mg / L.

3. The method for enhancing the co-fermentation of waste grease and excess sludge to produce acid by sulfur reduction according to claim 1, characterized in that: In step 2), the ratio of waste grease to sludge is 0.51 g / gTS.

4. The method for enhancing the co-fermentation of waste grease and excess sludge to produce acid by sulfur reduction according to claim 1, wherein: In step 3), the sulfide is at least one of sodium sulfate, sodium sulfite, sodium thiosulfate and sulfur.

5. The method for enhancing the co-fermentation of waste grease and excess sludge to produce acid by sulfur reduction according to claim 4, characterized in that: Control the dosing concentration of sulfur to be 1200 mgS / L.

6. The method for enhancing the co-fermentation of waste grease and excess sludge to produce acid by sulfur reduction according to claim 1, wherein: In step 4), introduce nitrogen into the reaction device to create an anaerobic environment, and the introduced amount of nitrogen is 2.5 times the volume of the reaction device.

7. The method for co-fermenting acid from sulfur-reducing enhanced waste grease and excess sludge according to claim 1, characterized in that: In step 1), the method for treating the excess sludge is: wash and filter the excess sludge to remove large - particle impurities.

8. The method for enhancing the co-fermentation of waste grease and excess sludge to produce acid by sulfur reduction according to claim 1, characterized in that: In step 4), the reaction temperature is 35 °C and the pH value is 9 ± 0.

5.

9. The method for enhancing the co-fermentation of waste grease and excess sludge to produce acid by sulfur reduction according to claim 1, wherein: In step 4), a stirring mechanism is provided in the reaction device, and the rotation speed is 400 ± 550 rpm.

10. The method for enhancing the co-fermentation of waste grease and excess sludge to produce acid by sulfur reduction according to claim 1, characterized in that: In step 4), the reaction process is in a light - shielding environment.

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