Method for synchronously treating sludge lysate and microplastics by using sulfate free radicals

Abstract

The invention provides a method for synchronously treating sludge lysate and microplastics by using sulfate free radicals, and belongs to the technical field of sludge treatment. The method comprises the following steps: naturally settling residual sludge to obtain a sludge sample; then mixing the sludge sample with ferrate and sulfite, and performing pretreatment to obtain pretreated sludge; and finally, mixing the pretreated sludge, fresh sludge and micro-plastics, and carrying out anaerobic fermentation. The Fe (VI) / S (IV) free radical advanced oxidation method is adopted to treat the excess sludge and destroy cell walls and extracellular polymeric substances (EPS), so that intracellular water and EPS combined water are released, sludge solubilization is promoted, the concentration of volatile acid in the excess sludge fermentation process is obviously increased, and the proportion of acetic acid in the total volatile acid is increased. Meanwhile, micro-plastics in the sludge are effectively aged and depolymerized under the action of microorganisms and free radicals in the process.

Description

Technical Field

[0001] The present invention relates to the technical field of sludge treatment, and in particular to a method for synchronously treating sludge lysis and microplastics by utilizing sulfate free radicals. Background Art

[0002] Microplastics (MPs) refer to plastics with a diameter of less than 5 mm. In recent years, they have attracted widespread attention due to their potential physical and chemical toxicity. In addition, the leachate released from MPs contains plasticizers such as phthalates and bisphenol A, as well as other toxic substances, which can also cause damage to the ecological environment. Therefore, how to reduce the content of microplastics in organic waste is of great significance for alleviating microplastic pollution and improving the resource utilization of organic waste.

[0003] Anaerobic fermentation of sludge is an effective way to utilize sludge resources. It can not only reduce the volume of sludge, but also convert the organic matter in the sludge into high value-added products such as volatile short-chain fatty acids (SCFAs) and methane, reducing the consumption of non-renewable fuels and achieving sustainable development. Many organic pollutants and heavy metals in organic solid waste can be effectively degraded during anaerobic fermentation, including microplastics. The depolymerization process of microplastics generally includes biological and non-biological effects. Free radicals are an important driving force for the transformation of pollutants in the environment. In the presence of active free radicals (such as SO4· - ), MPs can be decomposed into environmentally friendly organic intermediates or eventually mineralized into CO 2 and ·OH. Free radicals can also promote the oxidation of microplastic surfaces and accelerate their aging. While MPs are depolymerizing or aging, they will also produce leaching products such as plastic monomers, oligomers and additives, which will inhibit the anaerobic fermentation of sludge. Therefore, it is of great significance to provide a method for the simultaneous treatment of sludge lysis and microplastics using sulfate radicals. Summary of the invention

[0004] The purpose of the present invention is to provide a method for simultaneously treating sludge lysis and microplastics using sulfate free radicals, so as to solve the problems of low sludge carbon source conversion efficiency and pollution caused by microplastics in the prior art.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a method for simultaneously treating sludge lysis and microplastics by using sulfate free radicals, comprising the following steps:

[0007] (1) allowing the excess sludge to settle naturally to obtain a sludge sample;

[0008] (2) mixing the sludge sample with ferrate and sulfite and performing pretreatment to obtain pretreated sludge;

[0009] (3) The pretreated sludge, fresh sludge and microplastics are mixed and then subjected to anaerobic fermentation.

[0010] Preferably, in the step (1), the natural sedimentation temperature is 2-6°C, and the natural sedimentation time is 20-30 hours; the concentration of TSS in the sludge sample is 15-25 g / L, and the concentration of VSS is 8-12 g / L.

[0011] Preferably, in the step (1), the supernatant is discharged after natural sedimentation to obtain a sludge sample.

[0012] Preferably, in the step (2), the dosage of sulfite is 0.5-2 mmol / g-TSS; and the molar ratio of Fe(VI) in the ferrate to S(IV) in the sulfite is 1-3:1.

[0013] Preferably, in step (2), the pretreatment time is 20 to 28 hours.

[0014] Preferably, in step (3), the volume ratio of pretreated sludge to fresh sludge is 8 to 12:1; and the mass content of the microplastics is 0.2 to 0.8%.

[0015] Preferably, in step (3), the anaerobic fermentation is carried out under neutral conditions, and the fermentation tank is flushed with nitrogen before the anaerobic fermentation.

[0016] Preferably, the nitrogen flushing time of the fermentation tank is 10 to 20 minutes.

[0017] Preferably, in step (3), during anaerobic fermentation, the rotation speed is 110-120 rpm, the temperature is 33-37° C., and the time of anaerobic fermentation is 1-10 days.

[0018] Beneficial effects of the present invention:

[0019] (1) The present invention uses ferrate to activate sulfite to treat excess sludge, generating non-selective free radicals SO4· - Destroying cell walls and extracellular polymers releases intracellular water and extracellular polymer bound water, promoting sludge solubilization and the production of short-chain volatile fatty acids, significantly increasing the concentration of volatile acids during residual sludge fermentation and the proportion of acetic acid in total volatile acids. At the same time, promoting the depolymerization and aging of microplastics through microbial and free radical action is of great significance for reducing microplastic pollution and improving the efficiency of sludge resource utilization.

[0020] (2) After anaerobic fermentation, the PE-MPs at 2924, 2851, 1630, 1471 and 719 cm -1The spectral intensity at the position of PE-MPs weakened and the chemical peak position shifted to a certain extent, which indicated that PE-MPs underwent a certain degree of depolymerization and aging. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a graph showing the relationship between the volatile acid concentration and the fermentation time in Example 1 and Comparative Examples 1 to 5;

[0022] Figure 2 The figure is a comparison chart of the percentage content of each volatile acid in Example 1 and Comparative Examples 1 to 5 at 6 days of fermentation;

[0023] Figure 3 ] are infrared spectra of the PE-MPs after fermentation and the PE-MPs without any treatment in Example 2, Comparative Example 2 and Comparative Example 6, wherein MPs corresponds to the infrared spectra of PE-MPs. DETAILED DESCRIPTION

[0024] The present invention provides a method for simultaneously treating sludge lysis and microplastics by using sulfate free radicals, comprising the following steps:

[0025] (1) allowing the excess sludge to settle naturally to obtain a sludge sample;

[0026] (2) mixing the sludge sample with ferrate and sulfite and performing pretreatment to obtain pretreated sludge;

[0027] (3) The pretreated sludge, fresh sludge and microplastics are mixed and then subjected to anaerobic fermentation.

[0028] In the present invention, the excess sludge is preferably sieved and then subjected to natural sedimentation.

[0029] In the present invention, the pretreated sludge, fresh sludge and microplastics are mixed and then subjected to anaerobic fermentation, wherein the fresh sludge is rich in active microorganisms and can metabolize the pretreated sludge. This method can effectively improve the metabolic activity of the sludge.

[0030] In the present invention, in the step (1), the natural sedimentation temperature is 2-6°C, preferably 3-5°C, and more preferably 4°C; the natural sedimentation time is 20-30h, preferably 22-28h, and more preferably 24-26h; the TSS concentration in the sludge sample is 15-25g / L, preferably 18-22g / L, and more preferably 19-21g / L; the VSS concentration is 8-12g / L, and more preferably 9-11g / L.

[0031] In the present invention, in the step (1), the supernatant is discharged after natural sedimentation to obtain a sludge sample.

[0032] In the present invention, in the step (2), the dosage of sulfite is 0.5-2 mmol / g-TSS, preferably 0.8-1.5 mmol / g-TSS, and more preferably 1.0-1.2 mmol / g-TSS; the molar ratio of Fe(VI) in the ferrate to S(IV) in the sulfite is 1-3:1, preferably 1-2:1, and more preferably 1:1.

[0033] In the present invention, the sulfite is preferably sodium sulfite; and the ferrate is preferably potassium ferrate.

[0034] Other types of sodium sulfite and potassium ferrate can achieve the same effect. Considering the low pollution and low price, sodium sulfite and potassium ferrate are preferred.

[0035] In the present invention, in step (2), the pretreatment time is 20 to 28 hours, preferably 22 to 26 hours, and more preferably 24 hours.

[0036] In the present invention, in step (3), the volume ratio of pretreated sludge to fresh sludge is 8 to 12:1, preferably 9 to 11:1, and more preferably 10:1; the mass content of the microplastics is 0.2 to 0.8%, preferably 0.3 to 0.7%, and more preferably 0.4 to 0.5%.

[0037] In the present invention, the particle size of the microplastic is 100 to 200 μm, preferably 120 to 180 μm, and more preferably 150 μm.

[0038] In the present invention, in step (3), anaerobic fermentation is carried out under neutral conditions, and the fermentation tank is flushed with nitrogen before anaerobic fermentation.

[0039] In the present invention, the nitrogen flushing time of the fermentation tank is 10 to 20 minutes, preferably 12 to 18 minutes, and more preferably 15 minutes.

[0040] In the present invention, in step (3), the rotation speed during anaerobic fermentation is 110-120 rpm, preferably 112-118 rpm, and more preferably 115 rpm; the temperature is 33-37°C, preferably 34-36°C, and more preferably 35°C; the time of anaerobic fermentation is 1-10 d, preferably 2-8 d, and more preferably 4-6 d.

[0041] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0042] Example 1

[0043] Fresh residual sludge from the secondary sedimentation tank of Zhengyang Sewage Treatment Plant in Jinzhong City was passed through a 100-mesh sieve and allowed to settle naturally at 4°C for 24 hours. The supernatant was then discharged to obtain a sludge sample. The TSS and VSS in the sludge sample were 20.6 g / L and 10.16 g / L.

[0044] Take 300 mL of the sludge sample obtained above, add potassium ferrate and sodium sulfite to pretreat the sludge sample, wherein the addition amount of sodium sulfite is 1 mmol / g-TSS, and the molar ratio of Fe(VI) to S(IV) is 1:1. After addition, mechanical stirring is performed for 10 minutes to mix it evenly, and then pretreated for 24 hours to obtain pretreated sludge.

[0045] Powdered polyethylene (PE) microplastics (average particle size of 150 μm) were selected and placed in an oven at 65° C. to dry for 1 h before use.

[0046] The pretreated sludge and the fresh sludge in the secondary sedimentation tank of Zhengyang Sewage Treatment Plant were mixed in a volume ratio of 10:1, and transferred to an anaerobic fermentation tank with a volume of 500 mL (the anaerobic fermentation tank was equipped with two sampling tubes, one for collecting the gas produced by fermentation and the other for collecting the fermentation liquid, and the tubes were located below the liquid surface). Polyethylene microplastics (PE-MPs) were added to make the mass content of PE-MPs 0.5%, and then the pH value was adjusted to 7. The anaerobic fermentation tank was flushed with nitrogen for 15 minutes. Finally, the anaerobic fermentation tank was sealed and placed in an air bath shaker. Anaerobic fermentation was carried out at a speed of 115 rpm and a temperature of 35°C for 10 days. Sampling was taken regularly every day, and the sampling was marked as Fe(VI) / S(IV)+MPs.

[0047] Example 2

[0048] Fresh residual sludge from the secondary sedimentation tank of Zhengyang Sewage Treatment Plant in Jinzhong City was passed through a 100-mesh sieve and allowed to settle naturally at 4°C for 24 hours. The supernatant was then discharged to obtain a sludge sample. The TSS and VSS in the sludge sample were 20.6 g / L and 10.16 g / L.

[0049] Take 300 mL of the sludge sample obtained above, add potassium ferrate and sodium sulfite to pretreat the sludge sample, wherein the addition amount of sodium sulfite is 0.5 mmol / g-TSS, and the molar ratio of Fe(VI) to S(IV) is 1:1. After addition, mechanical stirring is performed for 10 minutes to mix it evenly, and then pretreated for 28 hours to obtain pretreated sludge.

[0050] Powdered polyethylene (PE) microplastics (average particle size of 150 μm) were selected and placed in an oven at 65° C. to dry for 1 h before use.

[0051] The pretreated sludge and fresh sludge were mixed in a volume ratio of 8:1 and transferred to an anaerobic fermentation tank with a volume of 500 mL (the anaerobic fermentation tank was equipped with two sampling tubes, one for collecting the gas produced by fermentation and the other for collecting the fermentation liquid, and the tubes were located below the liquid surface). Polyethylene microplastics (PE-MPs) were added to make the mass content of PE-MPs 0.8%. Then the pH value was adjusted to 7, and the anaerobic fermentation tank was flushed with nitrogen for 20 minutes. Finally, the anaerobic fermentation tank was sealed and placed in an air bath shaker for anaerobically fermentation at a speed of 120 rpm and a temperature of 33°C for 10 days.

[0052] Example 3

[0053] Fresh residual sludge from the secondary sedimentation tank of Zhengyang Sewage Treatment Plant in Jinzhong City was passed through a 100-mesh sieve and allowed to settle naturally at 4°C for 24 hours. The supernatant was then discharged to obtain a sludge sample. The TSS and VSS in the sludge sample were 20.6 g / L and 10.16 g / L.

[0054] Take 300 mL of the sludge sample obtained above, add potassium ferrate and sodium sulfite to pretreat the sludge sample, wherein the addition amount of sodium sulfite is 1.5 mmol / g-TSS, and the molar ratio of Fe(VI) to S(IV) is 1:1. After addition, mechanical stirring is performed for 10 minutes to mix it evenly, and then pretreated for 20 hours to obtain pretreated sludge.

[0055] Powdered polyethylene (PE) microplastics (average particle size of 150 μm) were selected and placed in an oven at 65° C. to dry for 1 h before use.

[0056] The pretreated sludge and fresh sludge were mixed in a volume ratio of 12:1 and transferred to an anaerobic fermentation tank with a volume of 500 mL (the anaerobic fermentation tank was equipped with two sampling tubes, one for collecting the gas produced by fermentation and the other for collecting the fermentation liquid, and the tubes were located below the liquid surface). Polyethylene microplastics (PE-MPs) were added to make the mass content of PE-MPs 0.2%. Then the pH value was adjusted to 7, and the anaerobic fermentation tank was flushed with nitrogen for 20 minutes. Finally, the anaerobic fermentation tank was sealed and placed in an air bath shaker for anaerobically fermentation at a speed of 110 rpm and a temperature of 37°C for 10 days.

[0057] Comparative Example 1

[0058] Fresh residual sludge from the secondary sedimentation tank of Zhengyang Sewage Treatment Plant in Jinzhong City was passed through a 100-mesh sieve and allowed to settle naturally at 4°C for 24 hours. The supernatant was then discharged to obtain a sludge sample. The TSS and VSS in the sludge sample were 20.6 g / L and 10.16 g / L.

[0059] The sludge sample obtained above was transferred to an anaerobic fermentation tank with a volume of 500 mL (the anaerobic fermentation tank was equipped with two sampling tubes, one for collecting the gas produced by fermentation and the other for collecting the fermentation liquid), and then the pH value was adjusted to 7.0, and the anaerobic fermentation tank was flushed with nitrogen for 20 minutes. Finally, the anaerobic fermentation tank was sealed and placed in an air bath shaker for anaerobic fermentation at a speed of 120 rpm and a temperature of 30°C for 10 days. Sampling was taken regularly every day, and the sampling was marked as Control.

[0060] Comparative Example 2

[0061] Fresh residual sludge from the secondary sedimentation tank of Zhengyang Sewage Treatment Plant in Jinzhong City was passed through a 100-mesh sieve and allowed to settle naturally at 4°C for 24 hours. The supernatant was then discharged to obtain a sludge sample. The TSS and VSS in the sludge sample were 20.6 g / L and 10.16 g / L.

[0062] Powdered polyethylene (PE) microplastics (average particle size of 150 μm) were selected and placed in an oven at 65° C. to dry for 1 h before use.

[0063] The sludge sample obtained above was transferred to an anaerobic fermentation tank with a volume of 500 mL (the anaerobic fermentation tank was equipped with two sampling tubes, one for collecting the gas produced by fermentation and the other for collecting the fermentation liquid), and polyethylene microplastics (PE-MPs) were added to make the mass content of PE-MPs 0.5%. Then the pH value was adjusted to 7, and the anaerobic fermentation tank was flushed with nitrogen for 15 minutes. Finally, the anaerobic fermentation tank was sealed and placed in an air bath shaker. Anaerobic fermentation was carried out at a speed of 115 rpm and a temperature of 35°C for 10 days. Sampling was taken regularly every day and the samples were marked as MPs.

[0064] Comparative Example 3

[0065] The difference from Example 1 is that no polyethylene microplastics are added, other conditions are the same, and the sampling is marked as Fe(VI) / S(IV).

[0066] Comparative Example 4

[0067] The difference from Example 1 is that potassium ferrate is not added, other conditions are the same, and the sample is marked as S(IV)+MPs.

[0068] Comparative Example 5

[0069] The difference from Example 1 is that sodium sulfite is not added, other conditions are the same, and the sample is marked as Fe(VI)+MPs.

[0070] Comparative Example 6

[0071] The difference from Example 1 is that the pretreated sludge is directly transferred to an anaerobic fermentation tank with a volume of 500 mL without mixing with fresh sludge, and other conditions are the same.

[0072] The above Example 1 and Comparative Examples 1 to 5 were sampled and tested at regular intervals to obtain a relationship diagram between the concentration of volatile acid and fermentation time during the entire fermentation process (see Figure 1 ),from Figure 1 It can be seen that, regardless of the presence of MPs, the concentration of volatile acids increases with the fermentation time and reaches a peak on the sixth day. Compared with Comparative Example 1 (Control) and Comparative Example 2 (MPs), the concentration of volatile acids is significantly increased after Fe(VI) / S(IV) pretreatment (corresponding to Comparative Example 3), while the concentration of short-chain fatty acids (SCFAs) in Fe(VI) / S(IV)+MPs (corresponding to Example 1) is slightly lower than that in Comparative Example 3 under the condition of MPs. This may be because at high MPs concentrations, microbial and enzyme activities are inhibited, and the production of SCFAs is affected to a certain extent. When the anaerobic fermentation time is 6 days, the concentration of the Fe(VI) / S(IV)+MPs group is 2333.7 mg COD / L, which is 8.6% lower than that of the Fe(VI) / S(IV) pretreatment group alone, which is 3.93 times and 3.09 times that of the Control group and the MPs group, respectively.

[0073] Figure 2 The percentage of volatile acids in Example 1 and Comparative Examples 1 to 5 at 6 days of fermentation is compared. Figure 2 It can be seen that when the anaerobic fermentation time was 6 days, the percentage of acetic acid in the Fe(VI) / S(IV)+MPs group was 47.2%, while the percentage of acetic acid in the Control group and the MPs group was only 7.1% and 9.7%, respectively, an increase of 40.1% and 37.5%.

[0074] Figure 3 The infrared spectra of the PE-MPs after fermentation and the PE-MPs without any treatment in Example 2, Comparative Example 2 and Comparative Example 6 are shown in FIG. Figure 3 It can be seen that the functional group concentration at the corresponding position of the PE characteristic peak is reduced, which indicates that the PE-MPs polymer material has a certain degree of aging after Fe(VI) / S(IV) pretreatment, and PE-MPs has a certain degree of depolymerization. -1 The new peak that appears at belongs to the alcoholic hydroxyl group. Increasing the alcoholic hydroxyl group further improves the biodegradability of PE-MPs.

[0075] As can be seen from the above embodiments, the present invention provides a method for synchronously treating sludge lysis and microplastics using sulfate radicals. The present invention first allows the excess sludge to settle naturally to obtain a sludge sample; then the sludge sample is mixed with ferrate and sulfite and pretreated to obtain pretreated sludge; finally, the pretreated sludge, fresh sludge and microplastics are mixed and anaerobic fermentation is performed. The present invention uses a free radical advanced oxidation method of Fe(VI) / S(IV) to treat excess sludge, destroy cell walls and extracellular polymers (EPS), release intracellular water and EPS bound water, promote sludge solubilization, and significantly increase the concentration of volatile acids in the fermentation process of excess sludge, and increase the proportion of acetic acid in total volatile acids. At the same time, the microplastics in the sludge are also effectively aged and depolymerized by the action of microorganisms and free radicals in this process.

[0076] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for simultaneously treating sludge lysis and microplastics using sulfate free radicals, characterized in that: The steps include: (1) allowing the excess sludge to settle naturally to obtain a sludge sample; (2) mixing the sludge sample with ferrate and sulfite and performing pretreatment to obtain pretreated sludge; (3) The pretreated sludge, fresh sludge and microplastics are mixed and then subjected to anaerobic fermentation.

2. The method for simultaneously treating sludge lysis and microplastics using sulfate free radicals according to claim 1, characterized in that: In the step (1), the natural sedimentation temperature is 2-6° C., and the natural sedimentation time is 20-30 hours; the TSS concentration in the sludge sample is 15-25 g / L, and the VSS concentration is 8-12 g / L.

3. The method for simultaneously treating sludge lysis and microplastics using sulfate free radicals according to claim 1 or 2, characterized in that: In the step (1), after natural sedimentation, the supernatant is discharged to obtain a sludge sample.

4. The method for simultaneously treating sludge lysis and microplastics using sulfate free radicals according to claim 3, characterized in that: In the step (2), the dosage of sulfite is 0.5-2 mmol / g-TSS; the molar ratio of Fe(VI) in the ferrate to S(IV) in the sulfite is 1-3:

1.

5. The method for simultaneously treating sludge lysis and microplastics using sulfate free radicals according to claim 1, 2 or 4, characterized in that: In the step (2), the pretreatment time is 20 to 28 hours.

6. The method for simultaneously treating sludge lysis and microplastics using sulfate free radicals according to claim 5, characterized in that: In the step (3), the volume ratio of the pretreated sludge to the fresh sludge is 8 to 12:1; and the mass content of the microplastics is 0.2 to 0.8%.

7. The method for simultaneously treating sludge lysis and microplastics using sulfate radicals according to claim 4 or 6, characterized in that: In the step (3), the anaerobic fermentation is carried out under neutral conditions, and the fermentation tank is flushed with nitrogen before the anaerobic fermentation.

8. The method for simultaneously treating sludge lysis and microplastics using sulfate free radicals according to claim 7, characterized in that: The nitrogen flushing time of the fermentation tank is 10 to 20 minutes.

9. The method for simultaneously treating sludge lysis and microplastics using sulfate free radicals according to claim 6 or 8, characterized in that: In the step (3), during anaerobic fermentation, the rotation speed is 110-120 rpm, the temperature is 33-37° C., and the time of anaerobic fermentation is 1-10 days.

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