Modification method of activated carbon for waste oil excess sludge fermentation acid production system

Abstract

The invention relates to a modification method of activated carbon for a waste oil and excess sludge fermentation acid production system. Comprising the following steps: 1) grinding and screening activated carbon powder; 2) soaking the activated carbon powder obtained in the step 1) in a sodium hydrogen sulfite solution; (3) after soaking is finished, pouring out supernate in the step (2), and cleaning residual substances to obtain solid powder; and 4) drying the solid powder in the step 3) to obtain modified activated carbon powder. The modified activated carbon powder has a rich surface pore structure and a large specific surface area and can promote attachment and growth of microorganisms, so that enrichment of functional microorganisms in the anaerobic digestion process is facilitated. Compared with the unmodified activated carbon powder, the modified activated carbon powder has the advantage that the acid production performance is greatly improved by adding the modified activated carbon powder.

Description

Technical Field

[0001] The present invention relates to the technical field of waste oil treatment, and particularly relates to a modification method for activated carbon used in an acid production system by fermenting waste oil and surplus sludge. Background Art

[0002] With the rapid development of China's economy and the continuous improvement of residents' living standards, the catering industry has started to widely use edible oil in the food processing process. However, after high-temperature treatment, the physicochemical properties of the oil are prone to change, resulting in the loss of its edible value and ultimately being discarded. Waste oil has characteristics such as high organic load, high viscosity, strong hydrophobicity, poor biodegradability, easy acidification and deterioration, and high pollution risk.

[0003] Biodegradation is a commonly used disposal method for waste oil, which relies on anaerobic fermentation or microbial degradation to convert it into volatile fatty acids (VFAs) or methane. Surplus sludge is a by-product formed after the biochemical treatment of sewage, rich in essential nutrients such as nitrogen and phosphorus, and carrying a diverse microbial community, which has important potential in the resource utilization of organic waste. Compared with the problems such as carbon-nitrogen imbalance and single microbial community that may occur during the anaerobic fermentation of waste oil alone, the introduction of surplus sludge can effectively make up for the lack of nutrients and optimize the microbial community structure, thereby improving the stability and acid production efficiency of the fermentation system. In addition, surplus sludge is also rich in organic matter, including nutrients such as proteins, carbohydrates, humus, and nucleic acids. These easily biodegradable components are regarded as potential biological resources. Through anaerobic fermentation or anaerobic digestion, the organic matter in the sludge can be converted into short-chain fatty acids, hydrogen, or methane. In particular, acetic acid and propionic acid in VFAs are the key raw materials for synthesizing biodegradable plastics and are also high-quality external carbon sources in the process of biological nitrogen and phosphorus removal from sewage. Therefore, introducing surplus sludge into the waste oil anaerobic fermentation system can not only improve the degradation efficiency of organic matter and the accumulation of VFAs, but also reduce the risk of fermentation system instability caused by high oil load, thereby realizing the efficient resource utilization of waste oil, reducing its environmental pollution risk, promoting the co-treatment of sludge and organic waste, and promoting the sustainable development of the ecological environment.

[0004] However, a large amount of long-chain fatty acids produced by oil hydrolysis may accumulate, thereby inhibiting the activity of methanogens, especially acidophilic methanogens, and ultimately affecting the digestion effect. The presence of oil may have many impacts on the stable operation of the digestive system. Existing studies have shown that the addition of carbon-based materials can effectively improve the gas production performance and system operation stability of anaerobic fermentation of kitchen waste with high solid content. Activated carbon is a commonly used carbon-based material, but it is found in actual applications that the acid production rate of the system is still not particularly high. Therefore, a carbon-based material that can increase the acid production rate in the waste oil and surplus sludge fermentation acid production system is needed. Summary of the Invention

[0005] The object of the present invention is to provide a method for modifying activated carbon used in a waste grease and excess sludge fermentation acid production system to improve the acid production rate of the system.

[0006] To achieve the above object, a method for modifying activated carbon used in a waste grease and excess sludge acid production system of the present invention adopts the following technical solution: A method for modifying activated carbon used in a waste grease and excess sludge fermentation acid production system, comprising the following steps:

[0007] 1) Grind and screen the activated carbon powder;

[0008] 2) Immerse the activated carbon powder obtained in step 1) in a sodium bisulfite solution;

[0009] 3) After the immersion is completed, pour off the supernatant in step 2), wash the remaining material to obtain solid powder;

[0010] 4) Dry the solid powder in step 3) to obtain the modified activated carbon powder.

[0011] In step 1), after grinding, it is screened through a sieve with 100 - 200 meshes.

[0012] In step 2), the concentration of the sodium bisulfite solution is 50 mM.

[0013] In step 2), the immersion time is 10 - 36 h.

[0014] In step 3), after pouring off the supernatant, add pure water and stir, immerse again, then pour off the supernatant, and repeat three times.

[0015] The time for the second immersion is 0.5 - 1.5 h.

[0016] In step 4), it is dried in an oven at a temperature of 70 - 90 °C until constant weight, and then taken out.

[0017] The beneficial effects of the present invention: The modified activated carbon powder has a rich surface pore structure and a large specific surface area, which can promote the attachment and growth of microorganisms, thus facilitating the enrichment of functional microorganisms in the anaerobic digestion process. The addition of the modified activated carbon powder greatly improves the acid production performance compared with the unmodified activated carbon powder. Brief Description of the Drawings

[0018] Figure 1 is the dissolution of organic matter in each group of reactors;

[0019] Figure 2 is the trend of the cumulative amount of TVFA (total volatile fatty acids) changing with time;

[0020] Figure 3 The influence of different reactors on the acidification rate of the fermentation broth;

[0021] Figure 4 The change of VFA production rate (acid production rate) in different reactors. Specific implementation method

[0022] Example 1

[0023] 1) Grind and screen the activated carbon powder.

[0024] In this step, the purchased activated carbon is ground and then screened through a 150-mesh sieve.

[0025] 2) Put the activated carbon powder obtained in step 1) into a sodium bisulfite solution for soaking.

[0026] In this step, the soaking time is 24 h. The concentration of the sodium bisulfite solution is 50 mM (millimoles per liter). The specific preparation process is to weigh 2.6 g of sodium bisulfite and make up the volume to 500 ml with pure water. Weigh 10 g of activated carbon powder and soak it in 500 ml of a 50 mM sodium bisulfite solution for 24 hours.

[0027] 3) After the soaking is completed, pour off the supernatant in step 2), wash the remaining substance, and obtain solid powder.

[0028] In this step, after the soaking is completed, pour off the supernatant, then add pure water and stir, soak again, and then pour off the supernatant, repeating three times. The time for the second soaking is 1 h.

[0029] 4) Dry the solid powder in step 3) to obtain the modified activated carbon powder.

[0030] In this step, put the solid powder into an electrothermal forced-air drying oven for drying, the temperature is 80 °C, dry until constant weight, and then take it out to obtain the modified activated carbon powder.

[0031] Example 2

[0032] 1) Grind and screen the activated carbon powder.

[0033] In this step, the purchased activated carbon is ground and then screened through a 100-mesh sieve.

[0034] 2) Put the activated carbon powder obtained in step 1) into a sodium bisulfite solution for soaking.

[0035] In this step, the soaking time is 10 h. The concentration of the sodium bisulfite solution is 50 mM (millimoles per liter). The specific preparation process is to weigh 2.6 g of sodium bisulfite and make up the volume to 500 ml with pure water. Weigh 10 g of activated carbon powder and soak it in 500 ml of sodium bisulfite solution with a concentration of 50 mM for 10 hours.

[0036] 3) After the soaking is completed, pour out the supernatant in step 2), wash the remaining substances, and obtain solid powder.

[0037] In this step, after the soaking is completed, pour out the supernatant, then add pure water and stir, soak again, then pour out the supernatant, and repeat three times. The time for the second soaking is 0.5 h.

[0038] 4) Dry the solid powder in step 3) to obtain modified activated carbon powder.

[0039] In this step, put the solid powder into an electrothermal blast drying oven for drying, the temperature is 70 °C, dry until constant weight, then take it out to obtain modified activated carbon powder.

[0040] Example 3

[0041] 1) Grind and sieve the activated carbon powder.

[0042] In this step, grind the purchased activated carbon, and after grinding, sieve it through a 200-mesh sieve.

[0043] 2) Put the activated carbon powder obtained in step 1) into a sodium bisulfite solution for soaking.

[0044] In this step, the soaking time is 36 h. The concentration of the sodium bisulfite solution is 50 mM (millimoles per liter). The specific preparation process is to weigh 2.6 g of sodium bisulfite and make up the volume to 500 ml with pure water. Weigh 10 g of activated carbon powder and soak it in 500 ml of sodium bisulfite solution with a concentration of 50 mM for 36 hours.

[0045] 3) After the soaking is completed, pour out the supernatant in step 2), wash the remaining substances, and obtain solid powder.

[0046] In this step, after the soaking is completed, pour out the supernatant, then add pure water and stir, soak again, then pour out the supernatant, and repeat three times. The time for the second soaking is 1.5 h.

[0047] 4) Dry the solid powder in step 3) to obtain modified activated carbon powder.

[0048] In this step, put the solid powder into an electrothermal blast drying oven for drying, the temperature is 90 °C, dry until constant weight, then take it out to obtain modified activated carbon powder.

[0049] The modified activated carbon powder obtained in Experimental Example 1 was used for experiments, and the experimental parameters were adjusted for comparative analysis.

[0050] This experiment adopted a batch operation mode, with a single feeding for long-term fermentation. The fermentation cycle was 15 days. The sludge used in this experiment was taken from the excess sludge of the secondary sedimentation tank of Wulongkou Wastewater Treatment Plant in Zhengzhou City. After treatment, the final sludge concentration was controlled at 19 ± 0.3 g (specific sludge parameters are shown in Table 2). Edible oil was used instead of waste oil for the oil, and the oil concentration was 9.7 g / L. Sodium sulfate was used as the electron acceptor in the fermentation, with a concentration of 1200 mg S / L. The temperature was set at 35 °C, and the rotation speed was set at 200 ± 50 rpm. The pH was adjusted to 9 ± 0.1 throughout the process by a pH automatic control device. The activated carbon material was the purchased powdered activated carbon, which was ground and passed through a 150-mesh sieve. The chemical treatment method was to soak it in a 50 mM sodium bisulfite solution for 24 h, wash it three times with pure water, and then dry it to reduce the redox property of the activated carbon. After the reactor was installed, it was purged with nitrogen for 5 min to remove the air at the top of the reactor to create an anaerobic environment. During the experiment, sludge samples were collected every 1 day. Among them, the supernatant samples were centrifuged at high speed and filtered through a 0.45 μm microporous membrane (Jinteng) for index determination; the mixed liquor samples were directly stored frozen at -20 °C for subsequent analysis. The treatment process of the biological phase samples was as follows: after the samples were centrifuged to remove the supernatant, 2 mL of 40% (m / m) sterilized glycerol was added, and after thorough mixing, they were stored in a -20 °C refrigerator for subsequent research.

[0051] The anaerobic acid production experiment was carried out in a 500 mL anaerobic bottle with an effective volume of 500 mL. It was divided into five groups. The specific experimental design parameters are shown in Table 1.

[0052] Table 1

[0053]

[0054] Table 2

[0055]

[0056] Figure 1 It shows the dissolution of organic matter in each group of reactors. The substrate dissolution effects of groups R1 and R2 were the best, being 19715 mg / L and 16480 mg / L respectively, indicating that in these groups, the substrate dissolution rate was relatively high. The substrate dissolution effects of groups R2 and R4 were close, and the data showed that the redox functional groups of the activated carbon did not show an obvious influence during the substrate dissolution process.

[0057] Figure 2It is the trend of the cumulative amount of TVFA (total volatile fatty acids) changing with time. By comparing the results of different groups, it can be seen that adding sulfate significantly increases the acid production in the anaerobic fermentation of conditioned sludge, with an increase of 130%. In addition, adding activated carbon can also effectively increase the acid production, with an increase of 25%. When sulfate and activated carbon are used in combination, compared with the system with only sulfate added, the acid production of conditioned sludge further increases, with increases of 18.7% and 38.1% respectively. This indicates that the synergistic effect of sulfate and activated carbon has a significant promoting effect on increasing the acid production during anaerobic fermentation.

[0058] Figure 3 It is the influence of different reactors on the acidification rate of the fermentation broth. The acidification rate of the modified activated carbon reactor is ultimately 2.7% higher than that of the control group. The modified activated carbon may have changed its surface chemical properties, making it more suitable for the attachment and growth of microorganisms, thereby promoting the degradation of substrates and the accumulation of VFAs. Compared with the blank group, the acidification rate of R5 is effectively increased, indicating that activated carbon reduces the inhibition of LCFA and enhances the decomposition of waste grease, enabling it to be converted into VFAs more rapidly.

[0059] The VFA production rate (acid production rate) is one of the key indicators for evaluating the effect of anaerobic sludge fermentation, which reflects the efficiency of converting organic matter in sludge into acidic products. Figure 4 It is the change of the VFA production rate in different reactors. It can be seen that the waste grease used as a carbon source and the excess sludge ferment synergistically, increasing the acid production rate of the fermentation system. Due to its rich porous structure and good electrical conductivity, activated carbon enables more organic matter in the system to be converted into VFA, which is more obvious in the fermentation group with added waste grease.

Claims

1. A method for modifying activated carbon used in a waste grease and excess sludge fermentation acid production system, characterized in that, It includes the following steps: 1) Grind and screen the activated carbon powder; 2) Immerse the activated carbon powder obtained in step 1) in a sodium bisulfite solution; 3) After the immersion ends, pour off the supernatant in step 2), wash the remaining substances to obtain solid powder; 4) Dry the solid powder in step 3) to obtain the modified activated carbon powder.

2. The modification method of activated carbon for the waste grease surplus sludge fermentation acid production system according to claim 1, characterized in that: In step 1), after grinding, it is screened through a sieve with 100 - 200 meshes.

3. The modification method of activated carbon for the waste grease surplus sludge fermentation acid production system according to claim 1, characterized in that: In step 2), the concentration of the sodium bisulfite solution is 50 mM.

4. The modification method of activated carbon for the waste grease surplus sludge fermentation acid production system according to claim 1, characterized in that: In step 2), the immersion time is 10 - 36 h.

5. The modification method of activated carbon for the waste grease and surplus sludge fermentation acid production system according to claim 1, characterized in that: In step 3), after pouring off the supernatant, add pure water and stir, immerse again, then pour off the supernatant, and repeat three times.

6. The modification method of activated carbon for the waste grease surplus sludge fermentation acid production system according to claim 5, characterized in that: The time for the second immersion is 0.5 - 1.5 h.

7. The modification method of activated carbon for the waste grease surplus sludge fermentation acid production system according to claim 1, characterized in that: In step 4), it is dried in an oven at a temperature of 70 - 90 °C until constant weight, and then taken out.

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