Method for strengthening collaborative risk factor control in sludge recycling process

Abstract

The invention relates to a method for enhancing collaborative risk factor control in a sludge recycling process, in particular to a method for enhancing collaborative resistance gene risk control in anaerobic fermentation acid production of excess sludge through combined pretreatment of nano zero-valent iron and peracetic acid. The invention aims to solve the problem of resistance gene transfer in the sludge resource recycling process. The method comprises the following steps: naturally settling residual sludge, removing supernate to obtain concentrated sludge, and adding nano zero-valent iron and peracetic acid for combined pretreatment. And placing the treated sludge in a reaction container, aerating with nitrogen, sealing the reactor, and carrying out anaerobic fermentation in a constant-temperature oscillator. According to the invention, organic matters in the sludge can be converted into short-chain fatty acid, the structure of a resistance gene can be destroyed, and the abundance of the resistance gene in the sludge is reduced. Meanwhile, horizontal transfer of resistance genes in the sludge is inhibited, and the environmental risk is controlled. The method is applied to the field of organic solid waste resource utilization.

Description

Technical Field

[0001] The present invention relates to a method for strengthening the collaborative control of risk factors in the process of sludge resource utilization. Background Art

[0002] The wide adoption of the activated sludge process has led to a large accumulation of by-products, i.e., excess sludge. The excess sludge is complex in composition and has potential environmental risks. Its treatment and disposal face severe challenges, but the organic matter it contains makes it a potential raw material for resource recovery. Anaerobic fermentation, as an effective technology for converting waste into resources, can produce short-chain fatty acids that can be used as carbon sources for nitrogen and phosphorus removal to achieve in-situ carbon cycling. The presence of microbial extracellular polymers makes the dissolution and hydrolysis of organic matter the rate-limiting step of anaerobic fermentation. Advanced oxidation technology is widely used to promote the hydrolysis process of sludge by generating reactive species to decompose sludge flocs and destroy cell structures.

[0003] However, wastewater treatment plants are repositories of resistance genes, and more than 360 resistance genes have been identified in activated sludge. The destruction of cell structures by advanced oxidation technology will lead to the release of intracellular resistance genes. The resistance genes released into the liquid phase can adsorb on organic matter and be protected from degradation by nucleases. After being taken up by microorganisms and integrated into the genome, resistance genes can accelerate horizontal transfer through conjugation between cells. In addition, the oxidative stress brought by the reactive species generated by chemical oxidants will selectively enrich resistant bacteria with strong resistance, affecting the bacterial community and metabolic pathways of microorganisms, further enhancing the transfer frequency of resistance genes and aggravating environmental risks. Therefore, it is urgent to develop a technology for strengthening the collaborative control of resistance gene risks in the resource utilization process. Summary of the Invention

[0004] The purpose of the present invention is to solve the problem of the transfer of resistance genes in the process of sludge resource recovery, and provide a method for strengthening the collaborative control of risk factors in the process of sludge resource utilization.

[0005] The present invention relates to a method for strengthening the collaborative control of risk factors in the process of sludge resource utilization, and the specific method is as follows:

[0006] I. Naturally sediment the excess sludge from the secondary sedimentation tank of the wastewater treatment plant, discard the supernatant to obtain concentrated sludge, and reserve it after sieving;

[0007] II. Treat the concentrated sludge with nano-zero valent iron, and then add peracetic acid for stirring reaction treatment to complete the pretreatment of the sludge;

[0008] III. Place the pretreated sludge in a reaction vessel, aerate with nitrogen, then seal the reactor, and carry out anaerobic fermentation in a constant temperature shaker, thus completing.

[0009] Advantages of the Present Invention

[0010] (1) When treating excess sludge by combining nano zero-valent iron and peracetic acid, the organic free radicals and hydroxyl free radicals generated effectively damage the extracellular polymeric substances and cell membrane structures of the sludge, providing more organic carbon sources for anaerobic fermentation microorganisms, effectively shortening the optimal fermentation time, increasing the production of short-chain fatty acids, and enhancing the resource utilization efficiency of the sludge.

[0011] (2) The resistance genes in the sludge are effectively reduced during the pretreatment and anaerobic fermentation processes, and the abundance of mobile genetic elements that can mediate the horizontal transfer of resistance genes is also significantly reduced, reducing the environmental risks of sludge resource utilization. Description of the Drawings

[0012] Figure 1 is a schematic diagram of the production of short-chain fatty acids during anaerobic fermentation in the examples and comparative examples of the present invention;

[0013] Figure 2 is a schematic diagram of the components of short-chain fatty acids on the 4th day of anaerobic fermentation in the examples and comparative examples of the present invention;

[0014] Figure 3 is a schematic diagram of the absolute abundances of 8 resistance genes after the end of anaerobic fermentation in the examples and comparative examples of the present invention;

[0015] Figure 4 is a schematic diagram of the absolute abundances of 3 mobile genetic elements after the end of anaerobic fermentation in the examples and comparative examples of the present invention. Detailed Embodiments

[0016] Detailed Embodiment 1: A method for strengthening the collaborative control of risk factors in the sludge resource utilization process of the present embodiment is carried out according to the following steps:

[0017] 1. Naturally settle the excess sludge from the secondary sedimentation tank of the sewage treatment plant, discard the supernatant to obtain concentrated sludge, and reserve it after sieving;

[0018] 2. Treat the concentrated sludge with nano zero-valent iron, and then add peracetic acid for stirring reaction treatment to complete the pretreatment of the sludge;

[0019] 3. Place the pretreated sludge in a reactor, aerate with nitrogen, then seal the reactor, and carry out anaerobic fermentation in a constant temperature shaker to complete.

[0020] The strong oxidizing ability of peracetic acid can destroy the cell membrane structure, denature and kill microbial proteins, interfere with the metabolic process of bacteria, and kill pathogens. However, peracetic acid cannot completely destroy the plasmid DNA structure, and the remaining resistance genes may transfer drug-resistant genes to downstream bacterial populations through horizontal transfer. Nano-zero valent iron has the ability to adsorb and degrade antibiotics and resistance genes, can effectively reduce the selection pressure, inhibit the abundance of mobile genetic elements, and slow down the horizontal transfer process. In addition, nano-zero valent iron has a good activation effect on peracetic acid. Therefore, the hydroxyl radicals and organic radicals generated by the combined treatment of the two may more effectively destroy the substances inside the cells, provide more organic matter for the anaerobic fermentation process, destroy the structure of resistance genes and mobile genetic elements, alleviate horizontal transfer, and control environmental risks.

[0021] Specific Embodiment 2: The difference between this embodiment and Specific Embodiment 1 is that: in Step 1, the temperature of natural sedimentation is 2 - 6 °C, and the sedimentation time is 24 - 36 h. Others are the same as Specific Embodiment 1.

[0022] Specific Embodiment 3: The difference between this embodiment and Specific Embodiment 1 or 2 is that: in Step 2, the concentration of nano-zero valent iron is 50 - 200 mg / gVSS. Others are the same as Specific Embodiment 1 or 2.

[0023] Specific Embodiment 4: The difference between this embodiment and any one of Specific Embodiments 1 to 3 is that: in Step 2, the concentration of peracetic acid is 10 - 40 mg / gVSS. Others are the same as any one of Specific Embodiments 1 to 3.

[0024] Specific Embodiment 5: The difference between this embodiment and any one of Specific Embodiments 1 to 4 is that: in Step 2, the stirring speed is 100 - 400 rpm, and the treatment time is 30 - 45 min. Others are the same as any one of Specific Embodiments 1 to 4.

[0025] Specific Embodiment 6: The difference between this embodiment and any one of Specific Embodiments 1 to 5 is that: in Step 3, the temperature of anaerobic fermentation is 25 - 37 °C. Others are the same as any one of Specific Embodiments 1 to 5.

[0026] Specific Embodiment 7: The difference between this embodiment and any one of Specific Embodiments 1 to 6 is that: in Step 3, the time of anaerobic fermentation is 6 - 14 d. Others are the same as any one of Specific Embodiments 1 to 6.

[0027] Specific Embodiment 8: The difference between this embodiment and any one of Specific Embodiments 1 to 7 is that: in Step 3, nitrogen aeration is carried out for 15 min. Others are the same as any one of Specific Embodiments 1 to 7.

[0028] The content of the present invention is not limited to the content of the above-mentioned embodiments, and the combination of one or several specific embodiments can also achieve the purpose of the invention.

[0029] Example 1

[0030] A method for strengthening the collaborative control of risk factors in the process of sludge resource utilization in this example is as follows:

[0031] After the excess sludge was naturally settled at 4 - 6°C for 24 h, the supernatant was discarded to obtain the sludge. After sieving, it was stored at 4 - 6°C for standby. The volatile suspended solid concentration and total suspended solid concentration of the sludge used were measured to be 14.91 ± 0.27 g / L and 25.73 ± 0.55 g / L, respectively. A certain volume of sludge was taken in a beaker, and nano zero-valent iron was added to make its concentration reach 50 mg / g VSS. Then peracetic acid was added to make its concentration reach 10 mg / g VSS, and it was treated at 250 rpm for 45 min at room temperature to obtain the sludge pretreated by the combination of nano zero-valent iron and peracetic acid. The treated sludge was transferred to a reaction vessel, aerated with high-purity nitrogen for 15 min, and then the reactor was sealed and anaerobically fermented in a constant temperature shaker at 35°C. The whole fermentation cycle lasted for 14 d. After the sludge system was pretreated by the combination of nano zero-valent iron and peracetic acid, the optimal fermentation time was shortened to 4 days, and the short-chain fatty acid concentration reached the highest of 186.43 mg COD / g VSS ( Figure 1 ), and the acetic acid concentration reached 118.85 mg COD / g VSS ( Figure 2 ). After the anaerobic fermentation was completed, the sum of the absolute abundances of the 8 resistance genes sul1, sul2, tetA, tetM, strB, aadA1, blaOXA, and ermB widely present in the sludge was reduced to 3.30×10 7 copies / g dry sludge ( Figure 3 ), and the sum of the absolute abundances of the mobile genetic elements intI1, Tn916, and ISCR1 mediating the horizontal transfer of resistance genes was reduced to 3.13×10 6 copies / g dry sludge ( Figure 4 ).

[0032] Example 2

[0033] A method for strengthening the collaborative control of risk factors in the process of sludge resource utilization in this example is as follows:

[0034] After the excess sludge was naturally settled at 4 - 6 °C for 24 h, the supernatant was discarded to obtain the sludge. After sieving, it was stored at 4 - 6 °C for standby. The volatile suspended solid concentration and total suspended solid concentration of the sludge used were measured to be 14.91 ± 0.27 g / L and 25.73 ± 0.55 g / L, respectively. A certain volume of sludge was taken in a beaker, and nano zero - valent iron was added to make its concentration reach 100 mg / gVSS. Then peracetic acid was added to make its concentration reach 20 mg / gVSS, and it was treated at 250 rpm for 45 min at room temperature to obtain the sludge pretreated by the combination of nano zero - valent iron and peracetic acid. The treated sludge was transferred to a reaction vessel, aerated with high - purity nitrogen for 15 min, and then the reactor was sealed and anaerobically fermented in a constant - temperature shaker at 35 °C. The whole fermentation cycle lasted for 14 d. After the sludge system was pretreated by the combination of nano zero - valent iron and peracetic acid, the optimal fermentation time was shortened to 5 days, and the concentration of short - chain fatty acids reached the highest of 232.59 mgCOD / gVSS on the 5th day ( Figure 1 ). After anaerobic fermentation, the absolute abundances of 8 resistance genes, namely sul1, sul2, tetA, tetM, strB, aadA1, blaOXA and ermB, widely existing in the sludge were reduced to 3.77×10 7 copies / g dry sludge ( Figure 3 ), and the sum of the absolute abundances of mobile genetic elements intI1, Tn916 and ISCR1 mediating the horizontal transfer of resistance genes was reduced to 2.19×10 6 copies / g dry sludge ( Figure 4 ).

[0035] Example 3

[0036] In this example, a method for strengthening the collaborative control of risk factors in the sludge resource utilization process is as follows:

[0037] The excess sludge was allowed to settle naturally at 4 - 6 °C for 24 h, and then the supernatant was discarded to obtain the sludge. After sieving, it was stored at 4 - 6 °C for later use. The volatile suspended solid concentration and total suspended solid concentration of the sludge used were measured to be 14.91 ± 0.27 g / L and 25.73 ± 0.55 g / L, respectively. A certain volume of the sludge was taken and placed in a beaker, and nano zero-valent iron was added to make its concentration reach 200 mg / g VSS. Then peracetic acid was added to make its concentration reach 40 mg / g VSS, and it was treated at 250 rpm at room temperature for 45 min to obtain the sludge pretreated with nano zero-valent iron and peracetic acid in combination. The treated sludge was transferred to a reaction vessel, aerated with high-purity nitrogen for 15 min, and then the reactor was sealed and anaerobically fermented in a constant-temperature shaker at 35 °C. The entire fermentation cycle lasted for 14 d. After the combined pretreatment of nano zero-valent iron and peracetic acid, the optimal fermentation time of the sludge system was shortened to 4 days, and the short-chain fatty acid concentration reached the highest of 305.51 mg COD / g VSS ( Figure 1 ) on the 4th day, and the acetic acid concentration reached 208.41 mg COD / g VSS ( Figure 2 ). After anaerobic fermentation, the absolute abundances of the 8 resistance genes sul1, sul2, tetA, tetM, strB, aadA1, blaOXA, and ermB widely present in the sludge decreased to 2.41×10 7 copies / g dry sludge ( Figure 3 ), and the sum of the absolute abundances of the mobile genetic elements intI1, Tn916, and ISCR1 that mediate the horizontal transfer of resistance genes decreased to 2.02×10 6 copies / g dry sludge ( Figure 4 ).

[0038] Control 1

[0039] The excess sludge was allowed to settle naturally at 4 - 6 °C for 24 h, and then the supernatant was discarded to obtain the sludge. After sieving, it was stored at 4 - 6 °C for later use. The volatile suspended solid concentration and total suspended solid concentration of the sludge used were measured to be 14.91 ± 0.27 g / L and 25.73 ± 0.55 g / L, respectively. A certain volume of the sludge was taken and placed in a beaker, and it was treated at 250 rpm at room temperature for 45 min to obtain the sludge without chemical pretreatment. The treated sludge was transferred to a reaction vessel, aerated with high-purity nitrogen for 15 min, and then the reactor was sealed and anaerobically fermented in a constant-temperature shaker at 35 °C. The entire fermentation cycle lasted for 14 d. The optimal fermentation time of the sludge without chemical pretreatment was the 6th day, and the short-chain fatty acid concentration reached 79.44 mg COD / g VSS ( Figure 1)。After anaerobic fermentation, the absolute abundances of eight resistance genes, sul1, sul2, tetA, tetM, strB, aadA1, blaOXA, and ermB, which are widely present in the sludge, were 7.54×10 7 copies / g dry sludge( Figure 3 ), and the sum of the absolute abundances of mobile genetic elements intI1, Tn916, and ISCR1 that mediate the horizontal transfer of resistance genes was 8.19×10 6 copies / g dry sludge( Figure 4 ).

[0040] Comparative Example 2

[0041] After the excess sludge was naturally settled at 4 - 6°C for 24 h, the supernatant was discarded to obtain the sludge. After sieving, it was stored at 4 - 6°C for later use. The volatile suspended solid concentration and total suspended solid concentration of the sludge used for determination were 14.91±0.27 g / L and 25.73±0.55 g / L, respectively. A certain volume of sludge was taken in a beaker, and peracetic acid was added to make its concentration reach 20 mg / g VSS. It was treated at 250 rpm for 45 min at room temperature to obtain peracetic acid-pretreated sludge. The treated sludge was transferred to a reaction vessel, aerated with high-purity nitrogen for 15 min, and then the reactor was sealed. Anaerobic fermentation was carried out in a constant temperature shaker at 35°C, and the whole fermentation cycle lasted for 14 d. The optimal fermentation time of the sludge system after peracetic acid pretreatment was the 4th day, and the short-chain fatty acid concentration reached the highest at 211.87 mg COD / g VSS( Figure 1 ), and the acetic acid concentration reached 113.17 mg COD / g VSS( Figure 2 ). After anaerobic fermentation, the sum of the absolute abundances of eight resistance genes, sul1, sul2, tetA, tetM, strB, aadA1, blaOXA, and ermB, which are widely present in the sludge, was 6.22×10 7 copies / g dry sludge( Figure 3 ), and the sum of the absolute abundances of mobile genetic elements intI1, Tn916, and ISCR1 that mediate the horizontal transfer of resistance genes was 5.77×10 6 copies / g dry sludge( Figure 4 ).

[0042] Comparative Example 3

[0043] After the excess sludge was naturally settled at 4 - 6 °C for 24 h, the supernatant was discarded to obtain the sludge. After sieving, it was stored at 4 - 6 °C for standby. The volatile suspended solid concentration and total suspended solid concentration of the sludge used were 14.91 ± 0.27 g / L and 25.73 ± 0.55 g / L, respectively. A certain volume of sludge was measured and placed in a beaker, and sludge biochar was added to make its concentration reach 100 mg / gVSS. Then peracetic acid was added to make its concentration reach 20 mg / gVSS, and it was treated at 250 rpm for 45 min at room temperature to obtain the sludge jointly pretreated with sludge biochar and peracetic acid. The treated sludge was transferred to a reaction vessel, aerated with high-purity nitrogen for 15 min, and then the reactor was sealed and anaerobically fermented in a constant-temperature shaker at 35 °C. The whole fermentation cycle lasted for 14 d. The optimal fermentation time of the sludge system jointly pretreated with sludge biochar and peracetic acid was 5 days, and the short-chain fatty acid concentration reached 205.50 mgCOD / gVSS on the 5th day ( Figure 1 ). After the anaerobic fermentation was completed, the absolute abundances of the eight resistance genes sul1, sul2, tetA, tetM, strB, aadA1, blaOXA, and ermB widely present in the sludge increased to 9.34×10 7 copies / g dry sludge ( Figure 3 ), and the sum of the absolute abundances of the mobile genetic elements intI1, Tn916, and ISCR1 that mediate the horizontal transfer of resistance genes increased to 9.17×10 6 copies / g dry sludge ( Figure 4 ).

[0044] It can be seen from the examples and comparative examples that the organic free radicals and hydroxyl free radicals generated by the combined treatment of nano zero-valent iron and peracetic acid in the examples can effectively destroy the extracellular polymeric substances and cell membrane structures of the sludge, provide organic matter for anaerobic fermentation microorganisms, increase the yield of short-chain fatty acids during anaerobic fermentation, and shorten the optimal fermentation time at the same time. The acetic acid is mainly enriched in the obtained fermentation broth, which can be used as an in-situ carbon source in the sewage treatment plant to promote the denitrification and phosphorus removal processes. In addition, the combined pretreatment can inhibit the conjugation transfer process, slow down the horizontal transfer of resistance genes in the sludge, and control the environmental risks.

Claims

1. A method for strengthening the control of collaborative risk factors in the process of sludge resource utilization, characterized in that, The method is as follows:

1. Naturally sediment the excess sludge from the secondary sedimentation tank of the sewage treatment plant, discard the supernatant to obtain concentrated sludge, and reserve it after sieving; 2. Treat the concentrated sludge with nano zero-valent iron, and then add peracetic acid for stirring reaction treatment to complete the pretreatment of the sludge; 3. Place the pretreated sludge in a reactor, aerate with nitrogen, then seal the reactor, and carry out anaerobic fermentation in a constant temperature shaker, that is, it is completed.

2. The method for strengthening the collaborative risk factor control in the sludge resource utilization process according to claim 1, wherein, In step 1, the temperature of natural sedimentation is 2 - 6°C, and the sedimentation time is 24 - 36 h.

3. A method for strengthening the collaborative control of risk factors in the process of sludge resource utilization according to claim 1, characterized in that, In step 2, the concentration of nano zero-valent iron is 50 - 200 mg / gVSS.

4. A method for strengthening the control of collaborative risk factors in the process of sludge resource utilization according to claim 1, characterized in that In step 2, the concentration of peracetic acid is 10 - 40 mg / gVSS.

5. A method for strengthening the collaborative risk factor control in the process of sludge resource utilization according to claim 1, characterized in that, In step 2, the stirring speed is 100 - 400 rpm, and the treatment time is 30 - 45 min.

6. The method for enhancing the collaborative risk factor control in the sludge resource utilization process according to claim 1, wherein, In step 3, the temperature of anaerobic fermentation is 25 - 37°C.

7. A method for enhancing the collaborative control of risk factors in the process of sludge resource utilization according to claim 1, characterized in that In step 3, the time of anaerobic fermentation is 6 - 14 d.

8. A method for strengthening the collaborative control of risk factors in the process of sludge resource utilization according to claim 1, characterized in that, In step 3, nitrogen aeration is carried out for 15 min.

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