Method for degrading tetracycline in sludge and improving anaerobic digestion efficiency

Abstract

The invention relates to a method for degrading tetracycline in sludge and improving anaerobic digestion efficiency. The method comprises the following steps: putting nano zero-valent iron into a sludge anaerobic reactor containing tetracycline, operating all the reactors in a constant-temperature oscillator at 37 DEG C at a rotating speed of 120 rpm, performing sealed culture for at least 30 days, and monitoring the change of pollutant indexes, tetracycline content and methane yield every day. According to the method, the methane production capacity and tetracycline degradation capacity of the reactor can be improved, various organic pollutants in the sludge can be effectively treated, the removal efficiency is high, and the method is simple. The method can effectively improve the resource utilization efficiency of the sludge, remove tetracycline in the sludge and reduce environmental pollution, and is suitable for efficient treatment of the sludge in a sewage treatment plant.

Description

Technical Field

[0001] The present invention belongs to the technical field of sludge treatment, and specifically relates to a method for degrading tetracycline in sludge and improving the efficiency of anaerobic digestion. The method utilizes nano zero-valent iron to strengthen the anaerobic digestion process, efficiently removes tetracycline in sludge, and increases methane production and removal of organic pollutants. Background Art

[0002] With the rapid development of industry and agriculture, antibiotics are widely used in agriculture, medicine and aquaculture, making antibiotic pollution a global environmental problem. Tetracycline is a broad-spectrum antibiotic that is used in large quantities due to its high efficiency. Its accumulation in the environment poses a potential threat to the ecosystem and human health. Sewage treatment plants are an important source of antibiotic pollution in the environment, but traditional sewage treatment technology has limited effect on the removal of antibiotics. A large amount of tetracycline is adsorbed into the sludge during sewage treatment. Studies have shown that the content of tetracycline in sludge is generally high, and its detection frequency is close to 100%, making it an important source of antibiotic pollution.

[0003] Traditional anaerobic digestion technology is widely used in sludge treatment, which can not only reduce the amount of sludge, but also achieve energy recovery through methane production. However, tetracycline has a significant inhibitory effect on the anaerobic digestion process. The antibacterial properties of tetracycline will affect hydrolysis, acidification and the activity of methanogens, thereby reducing the stability and treatment efficiency of the anaerobic digestion system. Studies have shown that when high concentrations of tetracycline are present in the anaerobic digestion system, methane production decreases by more than 70%, causing serious interference with the growth and metabolism of anaerobic microorganisms.

[0004] The present invention reduces the concentration of tetracycline in sludge and improves the efficiency of anaerobic digestion by adding a certain amount of nano zero-valent iron. Nano zero-valent iron can provide a more suitable growth environment for anaerobic microorganisms by reducing the redox potential, promoting hydrolysis acidification and methanogenesis. The corrosion products of nano zero-valent iron, such as divalent iron ions and hydrogen, can be used as essential nutrients for microbial growth, further enhancing the activity of the anaerobic digestion system. In addition, based on the strong reducing property of nano zero-valent iron, it also shows the advantage of promoting the removal of toxic pollutants. Although nano zero-valent iron has shown many advantages in the field of anaerobic digestion, it still faces some challenges during its use. For example, excessively high nano zero-valent iron concentrations may have toxic effects on microbial communities and inhibit the anaerobic digestion process. At the same time, the agglomeration of nano zero-valent iron may reduce its reaction activity, thereby affecting its removal effect on pollutants. Therefore, it is necessary to further explore and optimize the application conditions of nano zero-valent iron in sludge anaerobic digestion systems to balance its promoting effect and potential risks. In summary, the present invention proposes a method for anaerobic digestion of sludge combined with nano zero-valent iron. By optimizing the addition amount of nano zero-valent iron and the reaction conditions, the methane production and the operating stability of the anaerobic digestion system are significantly improved while achieving efficient removal of tetracycline. Summary of the invention

[0005] The object of the present invention is to provide a treatment method for degrading tetracycline in sludge by adding nano zero-valent iron into anaerobic reaction, which method can efficiently degrade the tetracycline content in sludge and improve the treatment effect of anaerobic reaction.

[0006] To achieve the above object, the technical solution of the present invention is:

[0007] A method for degrading tetracycline in sludge and improving anaerobic digestion efficiency, the method comprising the following steps:

[0008] (1) Take the sludge from the secondary sedimentation tank of the municipal sewage treatment plant for sedimentation;

[0009] (2) Screening the settled sludge to obtain activated sludge;

[0010] (3) subjecting a portion of the screened activated sludge to high temperature and high pressure thermal hydrolysis;

[0011] (4) anaerobic digestion sludge acclimation is performed on the sludge after high temperature and high pressure sludge thermal hydrolysis, and the feed and discharge are scheduled every day. The sludge after acclimation is used as inoculated sludge;

[0012] (5) After fully mixing the activated sludge and the inoculated sludge, a tetracycline concentrate is added to obtain a sludge mixture containing tetracycline;

[0013] (6) Adding nano-zero-valent iron to the tetracycline-containing sludge mixture obtained in step (5), and placing the sludge mixture into an anaerobic reactor for 30 days of anaerobic digestion.

[0014] The sedimentation in step (1) is gravity sedimentation, the sedimentation temperature is 4° C., and the sedimentation time is 24 hours.

[0015] In the step (2), a 10 mm sieve is used for sieving.

[0016] The conditions for the high temperature and high pressure thermal hydrolysis pretreatment in step (3) are 170° C. and 6 bar for 30 minutes.

[0017] In step (4), the sludge acclimation is carried out in a CSTR reactor at a temperature of 37° C. and a hydraulic retention time of 30 days. The acclimation is completed when the gas production tends to be stable.

[0018] In the step (5), the activated sludge and the inoculated sludge are mixed in a ratio of 1:1.

[0019] The reactor was initially filled with tetracycline at a concentration of 10 mg / L.

[0020] In the step (6), the particle size of nano zero-valent iron is 50 nm, the purity is 99.9%, and the optimal dosage is 1.0 g / L.

[0021] In the step (6), the anaerobic reactor is maintained in an anaerobic environment by filling with nitrogen and operating at a constant temperature of 37° C. and a rotation speed of 120 rpm for 30 days.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] (1) The present invention increases the removal rate of tetracycline to 90% by adding an appropriate amount of nano-zero-valent iron to the anaerobic digestion system, which is significantly better than the traditional anaerobic digestion technology. Under the condition of nano-zero-valent iron concentration of 1.0g / L, the methane production increased by 29.2%, providing a more efficient energy recovery pathway for sludge resource utilization.

[0024] (2) The present invention improves the operational stability of the anaerobic digestion system. The addition of nano-zero-valent iron effectively alleviates the inhibitory effect of tetracycline on anaerobic microorganisms by reducing the redox potential and promoting electron transfer, thereby enhancing the anti-interference ability of the anaerobic system.

[0025] (3) The process of the present invention is simple and environmentally friendly. The present invention does not require complicated equipment modification. It only needs to add an appropriate amount of nano zero-valent iron to the existing anaerobic digestion system, which has the characteristics of strong operability and low cost. At the same time, by improving the efficiency of pollutant degradation, the pollution of antibiotics to the ecosystem is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A schematic diagram of the connection structure of the equipment used in the method of the present invention;

[0027] Among them, 1-gravity sedimentation device, 2-pretreatment device, 3-anaerobic digestion and acclimatization device, 4-magnetic stirring device, 5-nano zero-valent iron adding device, 6-anaerobic digestion device, 7-biogas collection device. DETAILED DESCRIPTION

[0028] The present invention is further explained below in conjunction with the embodiments and drawings, but this is not intended to limit the scope of protection of the present application.

[0029] The invention discloses a method for degrading tetracycline in sludge and improving the efficiency of anaerobic digestion. The method comprises the following steps: placing residual sludge and anaerobic sludge in a reactor, adding nano zero-valent iron in an amount of 0.1 g to 5.0 g / L, and adjusting the initial pH value to 7; after driving oxygen and filling nitrogen in the reactor for 15 minutes, sealing the reaction bottle, culturing at a constant temperature for anaerobic digestion, and monitoring the organic pollutant index, methane production and tetracycline removal rate every day.

[0030] The initial sludge tetracycline concentration of the present invention is 10 mg / L, and the sludge organic matter indicators after high-temperature and high-pressure thermal hydrolysis are: SCOD: 12030 mg / L, polysaccharide; 2144 mg / L, protein; 4893 mg / L.

[0031] The particle size of the nano zero-valent iron of the present invention is 50 nm, the purity is 99.9%, and the optimal dosage is 1.0 g / L.

[0032] The equipment used in the present invention is as follows Figure 1 As shown, it includes a gravity sedimentation device 1, a pretreatment device 2, an anaerobic digestion acclimatization device 3, a magnetic stirring device 4, a nano zero-valent iron adding device 5, an anaerobic digestion device 6 and a biogas collection device 7.

[0033] Example 1

[0034] Step 1: After the sludge is taken out from the secondary sedimentation tank of the sewage treatment plant and allowed to stand at 4°C for 24 hours, the supernatant is discharged with a pipette and the sludge is filtered with a sieve with a pore size of 10 mm to remove impurities in the sludge. Finally, the treated sludge is stored at 4°C for subsequent experiments.

[0035] Step 2: Take a certain amount of treated sludge and treat it at 170℃ and 6 bar for 30 minutes. Store the treated sludge at 4℃ for subsequent experiments.

[0036] Step 3: Use a conical flask with a working volume of 500mL as a reactor, and add 200mL of domesticated inoculated sludge and 200mL of residual sludge treated with high temperature and high pressure to the reactor. After the sludge is mixed evenly, add tetracycline concentrate and stir with a magnetic stirrer at room temperature for 1h to wait for tetracycline adsorption equilibrium. The tetracycline concentration in the sludge is measured to be 10mg / L. Add 0.1g / L of nano zero-valent iron to the reactor, fill with 99.99% nitrogen for 15 minutes after stirring evenly, and then seal with a rubber stopper and aluminum cap. The reactor runs at a speed of 120rpm in a constant temperature oscillator at 37°C for 30 days. Ensure constant operating conditions to reduce the impact of external factors on the experiment itself.

[0037] The experimental results showed that the cumulative methane production in 30 days was 145 mL / g VS, and the removal rate of tetracycline was 82%.

[0038] Example 2

[0039] The steps of this embodiment are the same as those of embodiment 1, except that the dosage of nano zero-valent iron in this embodiment is 1.0 g / L.

[0040] Step 1: After the sludge is taken out from the secondary sedimentation tank of the sewage treatment plant and allowed to stand at 4°C for 24 hours, the supernatant is discharged with a pipette and the sludge is filtered with a sieve with a pore size of 10 mm to remove impurities in the sludge. Finally, the treated sludge is stored at 4°C for subsequent experiments.

[0041] Step 2: Take a certain amount of treated sludge and treat it at 170℃ and 6 bar for 30 minutes. Store the treated sludge at 4℃ for subsequent experiments.

[0042] Step 3: Use a conical flask with a working volume of 500mL as a reactor, and add 200mL of domesticated inoculated sludge and 200mL of residual sludge treated with high temperature and high pressure to the reactor. After the sludge is mixed evenly, add tetracycline concentrate and stir with a magnetic stirrer at room temperature for 1h to wait for tetracycline adsorption equilibrium. The tetracycline concentration in the sludge is measured to be 10mg / L. Add 1.0g / L of nano zero-valent iron to the reactor, fill it with 99.99% nitrogen for 15 minutes after stirring evenly, and then seal it with a rubber stopper and an aluminum cap. The reactor runs at a speed of 120rpm in a constant temperature oscillator at 37°C for 30 days. Ensure constant operating conditions to reduce the impact of external factors on the experiment itself.

[0043] The experimental results showed that the cumulative methane production in 30 days was 168 mL / g VS, and the removal rate of tetracycline was 87%.

[0044] Example 3

[0045] The steps of this embodiment are the same as those of embodiment 1, except that the dosage of nano zero-valent iron in this embodiment is 5.0 g / L.

[0046] Step 1: After the sludge is taken out from the secondary sedimentation tank of the sewage treatment plant and allowed to stand at 4°C for 24 hours, the supernatant is discharged with a pipette and the sludge is filtered with a sieve with a pore size of 10 mm to remove impurities in the sludge. Finally, the treated sludge is stored at 4°C for subsequent experiments.

[0047] Step 2: Take a certain amount of treated sludge and treat it at 170℃ and 6 bar for 30 minutes. Store the treated sludge at 4℃ for subsequent experiments.

[0048] Step 3: Use a conical flask with a working volume of 500mL as a reactor, and add 200mL of domesticated inoculated sludge and 200mL of residual sludge treated with high temperature and high pressure to the reactor. After the sludge is mixed evenly, add tetracycline concentrate and stir with a magnetic stirrer at room temperature for 1h to wait for tetracycline adsorption equilibrium. The tetracycline concentration in the sludge is measured to be 10mg / L. Add 5.0g / L of nano zero-valent iron to the reactor, fill with 99.99% nitrogen for 15 minutes after stirring evenly, and then seal with a rubber stopper and aluminum cap. The reactor runs at a speed of 120rpm in a constant temperature oscillator at 37°C for 30 days. Ensure constant operating conditions to reduce the impact of external factors on the experiment itself.

[0049] The experimental results showed that the cumulative methane production in 30 days was 148mL / gVS and the removal rate of tetracycline was 90%.

[0050] Comparative Example 1

[0051] The steps of this comparative example are the same as those of Example 1, except that nano zero-valent iron is not added in this comparative example.

[0052] Step 1: After the sludge is taken out from the secondary sedimentation tank of the sewage treatment plant and allowed to stand at 4°C for 24 hours, the supernatant is discharged with a pipette and the sludge is filtered with a sieve with a pore size of 10 mm to remove impurities in the sludge. Finally, the treated sludge is stored at 4°C for subsequent experiments.

[0053] Step 2: Take a certain amount of treated sludge and treat it at 170℃ and 6 bar for 30 minutes. Store the treated sludge at 4℃ for subsequent experiments.

[0054] Step 3: Use a conical flask with a working volume of 500 mL as a reactor, and add 200 mL of domesticated inoculated sludge and 200 mL of residual sludge treated with high temperature and high pressure to the reactor. After the sludge is mixed evenly, add tetracycline concentrate and stir with a magnetic stirrer at room temperature for 1 hour until the tetracycline adsorption equilibrium is reached. The tetracycline concentration in the sludge is measured to be 10 mg / L. Add 0.1 mg / L of nano zero-valent iron to the reactor, fill it with 99.99% nitrogen for 15 minutes after stirring evenly, and then seal it with a rubber stopper and an aluminum cap. The reactor runs at a constant temperature oscillator at 37°C at a speed of 120 rpm for 30 days. Ensure constant operating conditions to reduce the impact of external factors on the experiment itself.

[0055] The cumulative methane production in 30 days was 130 mL / g VS, and the removal rate of tetracycline was 65%.

[0056] In summary, the present invention improves the operational stability of the anaerobic digestion system by adding nano zero-valent iron, while reducing the concentration of polluting organic matter, improving the efficiency of methanogenesis, and efficiently removing tetracycline from sludge. It effectively improves the efficiency of sludge resource utilization, reduces antibiotic environmental pollution, and is suitable for efficient treatment of sludge in sewage treatment plants.

[0057] Any matters not described in the present invention are applicable to the prior art.

Claims

1. A method for degrading tetracycline in sludge and improving the efficiency of anaerobic digestion, characterized in that: The method comprises the following steps: (1) Take the sludge from the secondary sedimentation tank of the municipal sewage treatment plant for sedimentation; (2) Screening the settled sludge to obtain activated sludge; (3) subjecting a portion of the screened activated sludge to high temperature and high pressure thermal hydrolysis; (4) anaerobic digestion sludge acclimation is performed on the sludge after high temperature and high pressure sludge thermal hydrolysis, and the feed and discharge are scheduled every day. The sludge after acclimation is used as inoculated sludge; (5) After fully mixing the activated sludge and the inoculated sludge, a tetracycline concentrate is added to obtain a sludge mixture containing tetracycline; (6) Adding nano zero-valent iron to the tetracycline-containing sludge mixture obtained in step (5), and then placing the sludge mixture into an anaerobic reactor for 30 days of anaerobic digestion.

2. The method for degrading tetracycline in sludge and improving anaerobic digestion efficiency according to claim 1, characterized in that: The sedimentation in step (1) is gravity sedimentation, the sedimentation temperature is 4° C., and the sedimentation time is 24 hours.

3. The method for degrading tetracycline in sludge and improving anaerobic digestion efficiency according to claim 1, characterized in that: The high temperature and high pressure thermal hydrolysis pretreatment in step (3) is carried out at 170° C. and 6 bar for 30 minutes.

4. The method for degrading tetracycline in sludge and improving anaerobic digestion efficiency according to claim 1, characterized in that: In the step (4), the anaerobic digestion sludge acclimation is carried out in a CSTR reactor at a temperature of 37° C. and a hydraulic retention time of 30 days. The acclimation is completed when the gas production tends to be stable.

5. The method for degrading tetracycline in sludge and improving anaerobic digestion efficiency according to claim 1, characterized in that: In the step (5), the activated sludge and the inoculated sludge are mixed in a ratio of 1:

1.

6. The method for degrading tetracycline in sludge and improving anaerobic digestion efficiency according to claim 1, characterized in that: The initial concentration of tetracycline in the anaerobic reactor was 10 mg / L.

7. The method for degrading tetracycline in sludge and improving anaerobic digestion efficiency according to claim 1, characterized in that: In the step (6), the particle size of nano zero-valent iron is 50 nm, the purity is 99.9%, and the optimal dosage is 1.0 g / L.

8. The method for degrading tetracycline in sludge and improving anaerobic digestion efficiency according to claim 1, characterized in that: In the step (6), the anaerobic reactor is maintained in an anaerobic environment by filling with nitrogen and operating at a constant temperature of 37° C. and a rotation speed of 120 rpm for 30 days.

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