Method for removing perfluorinated compounds in sludge by activating peroxymonosulfate through dielectric barrier discharge

Abstract

The invention discloses a method for removing perfluorinated compounds in sludge by activating peroxymonosulfate through dielectric barrier discharge, which comprises the following steps: adjusting the total solid of the sludge to a proper range, adding the perfluorinated compounds, adding peroxymonosulfate into the sludge solution, and activating the peroxymonosulfate through dielectric discharge, according to the method, only peroxymonosulfate needs to be added, then a treated object is put into the dielectric barrier discharge reactor, and corresponding input voltage and current are adjusted; no medicament or catalyst needs to be added, no toxic by-product is generated, and electrons, free radicals and the like generated in the dielectric barrier discharge low-temperature plasma treatment process do not cause secondary pollution to the environment; the dielectric barrier discharge low-temperature plasma treatment and peroxymonosulfate have a remarkable synergistic effect, and the degradation efficiency of perfluorinated compounds in the sludge is high.

Description

Technical Field

[0001] The present invention belongs to the technical field of environmental pollution treatment, and relates to a method for removing perfluorinated compounds in sludge by activating peroxymonosulfate using dielectric barrier discharge. Background Art

[0002] Perfluorinated compounds (PFAS) are a class of formidable synthetic environmental chemicals. Due to their high thermal stability, chemical stability, and relatively stable C-F bonds, perfluorinated compounds can resist degradation by acids, bases, oxidants, reductants, and photolysis. Even more, they can resist biodegradation in microbial and metabolic processes and persist in the environment for a long time. Wastewater treatment plants (WWTPs) receive wastewater from residential, commercial, and industrial facilities. Due to the recalcitrance of perfluorinated compounds, they cannot be destroyed or removed during the treatment process in conventional wastewater treatment systems, leading to the accumulation of perfluorinated compounds in sewage sludge. Currently, the commonly used methods for removing perfluorinated compounds in sludge matrix include physical, biological, and chemical methods. Among them, the physical method mainly uses adsorbents to transfer perfluorinated compounds from the sludge system to the adsorbent, rather than truly mineralizing and degrading the pollutants, which has obvious limitations. The biological method itself has a relatively general efficiency for removing perfluorinated compounds, and culturing microorganisms and carrying out microbial reactions also require a long treatment cycle, so the biological method is not the most suitable method. The means of degrading perfluorinated compounds by chemical methods can be divided into thermal treatment and non-thermal treatment. Among them, using thermal degradation of pollutants requires a relatively high temperature, and a large amount of energy will be lost during the process. The non-thermal treatment method can achieve a high degradation effect while ensuring reasonable energy consumption. For example, the electrochemical method can degrade 95% of the perfluorinated compounds in the sludge matrix, and generates less heat with a high energy utilization rate. However, the electrochemical degradation of perfluorides requires special and expensive electrode materials, which limits its large-scale engineering application.

[0003] In recent years, many domestic and foreign scholars have studied the degradation of perfluorinated compounds by non-thermal plasma. Among them, it includes that atmospheric plasma can degrade 95% of PFOS and 90% of PFOA in the aqueous phase, and using non-thermal plasma to treat surface water can remove about 99% of the perfluorinated compounds in it. Although non-thermal plasma can degrade perfluorinated compounds in the aqueous phase, and the effect is relatively satisfactory. However, the effect of non-thermal plasma in degrading perfluorinated compounds in sludge is not ideal. Achieving a 50% sludge perfluoride degradation rate requires a large amount of energy consumption, which is mainly caused by factors such as the competition of sludge matrix for active free radicals and the limited reaction interface of traditional plasma reactors.

[0004] Therefore, it is an urgent problem to develop a technology with simple process, convenient operation method, low cost, low energy consumption, and capable of efficiently degrading perfluorinated compounds in sludge. Summary of the Invention

[0005] In order to more effectively degrade perfluorinated compounds in the sludge matrix, further reduce energy consumption for its application, and improve the energy utilization rate of the dielectric barrier discharge plasma technology, the present invention combines the dielectric barrier discharge plasma technology with an oxidant. The present invention further discovers that compared with other oxidants, peroxymonosulfate has higher oxidation ability and stronger organic matter decomposition ability. After being activated by plasma, the sulfur radicals released by peroxymonosulfate exhibit enhanced reactivity, thus promoting the degradation of organic pollutants. Therefore, in order to solve the foregoing technical problems, the present invention has developed a technology for degrading perfluorinated compounds in sludge by combining plasma and an oxidant.

[0006] Aiming at the deficiencies of the prior art, the present invention provides a method for removing perfluorinated compounds in sludge by activating peroxymonosulfate using dielectric barrier discharge, which includes the following steps:

[0007] (1) Take the excess sludge from the secondary sedimentation tank in the water treatment plant, adjust the total solid (TS) of the sludge to an appropriate range, and then add an appropriate amount of perfluorinated compounds thereto;

[0008] (2) Add peroxymonosulfate to the sludge solution and then activate it by dielectric discharge. During the discharge process, use a peristaltic pump to continuously pump the remaining sludge solution flowing out of the reactor to the discharge container, and introduce a background atmosphere thereto to degrade the perfluorinated compounds in the sludge, thus completing the process.

[0009] A non-equilibrium gas discharge through an insulating medium such as quartz or glass inserted into the discharge space is also called dielectric barrier corona discharge or silent discharge. The low-temperature plasma generated by dielectric barrier discharge will be accompanied by the synergistic effects of ultraviolet light radiation, high-energy electron bombardment, electromagnetic field, highly oxidative active particles, etc., all of which have the potential to activate peroxymonosulfate without introducing other chemical agents or catalytic materials. Therefore, the method of using plasma to activate peroxymonosulfate is an ideal method for solving the problem of removing perfluorinated compounds in sludge. The present invention adds peroxymonosulfate to the sludge solution containing perfluorinated compounds, and then performs dielectric barrier discharge low-temperature plasma treatment on it. Utilize the dielectric barrier discharge low-temperature plasma to generate electrons, light, heat, and magnetism, synergistically activate peroxymonosulfate, generate a series of reactive oxygen radicals, sulfate radicals, and hydroxyl radicals, and chemically react with the perfluorinated compounds in the sludge solution to degrade and mineralize the perfluorinated compounds.

[0010] Further, in step (1), the perfluorinated compounds are selected from one or more of perfluorooctanoic acid, perfluorooctane sulfonic acid and its salts, perfluoroheptanoic acid, perfluorobutane sulfonic acid and its salts, perfluorononanoic acid, perfluorohexyl sulfonic acid and its salts, perfluoropolyether, heptafluorobutyric acid, perfluoroalkyl phosphoric acid and hypophosphorous acid, and pentafluoropropionic acid.

[0011] Further, in step (1), the excess sludge is real excess sludge taken from a sewage treatment plant rather than a simulated sludge solution.

[0012] Further, in step (1), the total solids (TS) of the sludge solution is adjusted to 3 - 10 g / L with the sludge supernatant.

[0013] Further, the introduced background atmosphere is selected from one of air, nitrogen, oxygen, and argon, and the gas flow rate is 30 - 90 L / min; while dielectric barrier discharge occurs, air is introduced into the reaction system so that the sludge solution participates in the discharge reaction in the form of a liquid film.

[0014] Further, in step (2), a peristaltic pump is used to pump the sludge flowing out of the reactor back into the reaction device; ensuring that peroxymonosulfate can be fully discharged and activated, thereby effectively degrading perfluorinated compounds in the sludge solution.

[0015] Further, in step (2), the output power of the dielectric barrier discharge is 80 W - 120 W. When the output power is too low, the electric field strength is low and the electron density is low, which is not conducive to activating peroxymonosulfate to generate sulfate radicals, hydroxyl radicals, etc.; when the output power is too high, a large amount of energy is dissipated in the form of heat, and the energy utilization efficiency is reduced, which is not conducive to the efficient and energy-saving degradation of perfluorinated compounds.

[0016] Further, the molar ratio of the peroxymonosulfate to the perfluorinated compound is (4 - 22):1. When the concentration of peroxymonosulfate is too low, the concentration of carbon radicals generated is too small, which is not conducive to the removal of perfluorinated compounds; peroxymonosulfate itself has the role of a scavenger. When the concentration is too high, it will capture the free radicals already present in the system, resulting in a decrease in the efficiency of its degradation of perfluorinated compounds.

[0017] Further, in step (2), the treatment time of the dielectric barrier discharge non-thermal plasma is 10 - 180 minutes. If the treatment time is too short, the degradation rate of perfluorinated compounds is relatively low; if the treatment time is too long, the temperature of the treated solution will exceed the ambient temperature, causing thermal pollution, and the longer the treatment time, the total solids (TS) of the treated sludge solution will be too high, resulting in the accumulation of solid substances on the inner wall of the reaction vessel and ultimately causing breakdown and damage to the reactor.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] (1) The method of the present invention has a simple process and a convenient operation method. Only after adding peroxymonosulfate, the treatment object is placed in a dielectric barrier discharge reactor, and the corresponding input voltage and current are adjusted.

[0020] (2) When using the method of the present invention to treat perfluorinated compounds, no external agents or catalysts are required and no toxic by-products are generated. Electrons, free radicals, etc. generated during the treatment process of dielectric barrier discharge low-temperature plasma of the present invention will not cause secondary pollution to the environment;

[0021] (3) There is a significant synergistic effect between the dielectric barrier discharge low-temperature plasma treatment of the present invention and peroxymonosulfate. The degradation efficiency of perfluorinated compounds in sludge is relatively high, which can reduce the treatment cost, the reaction time is short, the treatment energy consumption is saved, and it has strong operability in actual engineering applications;

[0022] (4) The experimental sludge was extracted from real excess activated sludge in a real sewage treatment plant, simulating the removal process of perfluorinated compounds in sludge under real conditions, which fully illustrates the real feasibility of the experiment. Brief Description of the Drawings

[0023] Figure 1 It is the effect diagram of removing potassium perfluorooctane sulfonate in sludge by unactivated potassium peroxymonosulfate alone, dielectric barrier discharge plasma alone, and dielectric barrier discharge plasma-activated potassium peroxymonosulfate in Example 1;

[0024] Figure 2 It is the effect diagram of removing potassium perfluorooctane sulfonate in sludge by dielectric barrier discharge plasma-activated different doses of potassium peroxymonosulfate in Example 2. Detailed Embodiments

[0025] The present invention will be described in detail below with reference to the drawings and specific embodiments. This embodiment is implemented on the premise of the technical solution of the present invention, and the detailed implementation manner and specific operation process are given, but the protection scope of the present invention is not limited to the following embodiments.

[0026] In the following embodiments, unless otherwise specified for raw materials or treatment technologies, it means that the conventional commercially available raw material products or conventional treatment technologies in the art are used.

[0027] In the following embodiments, the dielectric barrier discharge low-temperature plasma treatment method is adopted. Among them, low-temperature plasma is a proper noun and does not specifically refer to a certain temperature. Plasma is the fourth state of matter after solid, liquid, and gas. When the applied voltage reaches the breakdown voltage, gas molecules are ionized to generate a mixture including electrons, ions, atoms, and atomic groups. Low-temperature plasma is a kind of plasma, different from high-temperature plasma. Although the electron temperature is very high during the discharge process of low-temperature plasma, the temperature of heavy particles is very low, and the whole system presents a low-temperature state, so it is called cold plasma, also called non-equilibrium plasma. If the electron temperature and the heavy particle temperature are about the same, it is thermal plasma, or equilibrium plasma.

[0028] The plasma source is a high-voltage power supply, and the high-voltage power supply used in the experiment was purchased from Nanjing Suman Technology Co., Ltd. The sludge was taken from the actual surplus sludge in the secondary sedimentation tank of Songjiang Western Sewage Treatment Plant. This sewage treatment plant treats 60% domestic sewage and 40% industrial wastewater. The physical and chemical properties of this actual surplus sludge are no different from those of the surplus sludge produced by most municipal sewage treatment plants and are representative.

[0029] Example 1

[0030] 5 mg of potassium perfluorooctane sulfonate was taken respectively to prepare three groups of 250 ml of sludge solutions with a concentration of 20 mg / L, and the total solid content of the sludge was 5 g / L, which were labeled as groups A, B, and C;

[0031] Among them, group A did not add potassium peroxymonosulfate and directly carried out dielectric barrier discharge treatment. While performing dielectric barrier discharge, air was introduced into the reactor, the air flow rate was 60 L / min, and the discharge power was 120 W;

[0032] Group B added 0.025 g of potassium peroxymonosulfate at a concentration of 0.1 g / L and did not perform discharge treatment;

[0033] Group C added 0.025 g of potassium peroxymonosulfate at a concentration of 0.1 g / L and then carried out dielectric barrier discharge treatment. While performing dielectric barrier discharge, air was introduced into the reactor, the air flow rate was 60 L / min, and the discharge power was 120 W.

[0034] During the reaction process of groups A, B, and C, a peristaltic pump was used to pump the sludge flowing out of the reactor back into the reaction device, and the rotational speed of the peristaltic pump was 40 r / min. The sampling times were 20, 40, 60, 80, and 100 min. The removal rates of potassium perfluorooctane sulfonate in the three groups of experiments at different times are as Figure 1 shown. It can be seen that the effect of removing potassium perfluorooctane sulfonate by activating potassium peroxymonosulfate with dielectric barrier discharge plasma in group C is the best, the reaction rate is the fastest. After 100 minutes of reaction, the removal rate of perfluorooctane sulfonate reaches 70%. In comparison, when only dielectric barrier discharge plasma was used for treatment for 100 minutes, the removal rate of potassium perfluorooctane sulfonate was 55%. The removal effect of unactivated potassium peroxymonosulfate alone on potassium perfluorooctane sulfonate was only 22%.

[0035] Example 2:

[0036] 5 mg of potassium perfluorooctane sulfonate was taken respectively to prepare fifteen groups of 250 ml of sludge solutions with a concentration of 20 mg / L, and the total solid content of the sludge was 5 g / L;

[0037] The first, second, and third groups were added with 0.0125 g of potassium peroxymonosulfate at 0.05 g / L, and the double dielectric barrier discharge treatment was carried out on the three groups of sludge-containing solutions. The discharge powers were 80 W, 96 W, and 120 W respectively. The fourth, fifth, and sixth groups were added with 0.025 g of potassium peroxymonosulfate at 0.1 g / L, and the double dielectric barrier discharge treatment was carried out on the three groups of sludge-containing solutions. The discharge powers were 80 W, 96 W, and 120 W respectively.

[0038] The seventh, eighth, and ninth groups were added with 0.0625 g of peroxymonosulfate at 0.25 g / L, and the double dielectric barrier discharge treatment was carried out on the three groups of sludge-containing solutions. The discharge powers were 80 W, 96 W, and 120 W respectively.

[0039] In the first, second, third, fourth, fifth, sixth, seventh, eighth, and ninth groups, air was introduced into the reactor while the dielectric barrier discharge was carried out. The air flow rate was 60 L / min. During the reaction process, the sludge flowing out of the reactor was pumped back into the reaction device by a peristaltic pump, and the rotational speed of the peristaltic pump was 40 r / min.

[0040] The thirteenth, fourteenth, and fifteenth groups were added with 0.0125 g, 0.025 g, and 0.0625 g of potassium peroxymonosulfate at 0.05 g / L, 0.1 g / L, and 0.25 g / L respectively, and the double dielectric barrier discharge treatment was not carried out on the three groups of sludge-containing solutions.

[0041] During the above fifteen groups of experiments, the change in the removal rate of perfluorooctane sulfonate was as Figure 2 shown. It can be seen that the effect of removing potassium perfluorooctane sulfonate in sludge by activating potassium peroxymonosulfate with double dielectric barrier discharge first became better with the increase of the dosage of potassium peroxymonosulfate, and then stagnated or decreased. The effect of removing perfluorooctane sulfonate in sludge by activating 0.1 g / L of potassium peroxymonosulfate with 80 W double dielectric barrier discharge was the best. When the reaction was carried out for 60 minutes, the removal rate of potassium perfluorooctane sulfonate reached 78%.

[0042] The above description of the embodiments is for the convenience of those of ordinary skill in the art to understand and use the invention. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative labor. Therefore, the present invention is not limited to the above embodiments, and the improvements and modifications made by those skilled in the art without departing from the scope of the present invention according to the disclosure of the present invention should be within the protection scope of the present invention.

Claims

1. A method for removing perfluorinated compounds in sludge by activating peroxymonosulfate using dielectric barrier discharge, characterized in that, It includes the following steps: (1) Take the excess sludge from the secondary sedimentation tank in the water treatment plant, adjust the total solids of the sludge to an appropriate range, and then add perfluorinated compounds thereto; (2) Add peroxymonosulfate to the sludge solution and then activate it by dielectric discharge. During the discharge process, use a peristaltic pump to continuously pump the excess sludge solution flowing out of the reactor to the discharge container, and introduce a background atmosphere thereto to degrade the perfluorinated compounds in the sludge, thus completing the process.

2. The method for removing perfluorinated compounds in sludge by activating peroxymonosulfate using dielectric barrier discharge according to claim 1, wherein, In step (1), the perfluorinated compounds are selected from one or more of perfluorooctanoic acid, perfluorooctane sulfonic acid and its salts, perfluoroheptanoic acid, perfluorobutane sulfonic acid and its salts, perfluorononanoic acid, perfluorohexyl sulfonic acid and its salts, perfluoropolyether, heptafluorobutyric acid, perfluoroalkyl phosphoric acid and hypophosphorous acid, and pentafluoropropionic acid.

3. The method for removing perfluorinated compounds in sludge by activating peroxymonosulfate using dielectric barrier discharge according to claim 1, characterized in that, In step (1), the excess sludge is the real excess sludge taken from the sewage treatment plant rather than a simulated sludge solution.

4. The method for removing perfluorinated compounds in sludge by activating peroxymonosulfate using dielectric barrier discharge according to claim 1, characterized in that, In step (1), adjust the total solids of the sludge solution to 3 - 10 g / L with the sludge supernatant.

5. The method for removing perfluorinated compounds in sludge by activating peroxymonosulfate using dielectric barrier discharge according to claim 1, wherein The introduced background atmosphere is selected from one of air, nitrogen, oxygen, and argon, and the gas flow rate is 30 - 90 L / min.

6. The method for removing perfluorinated compounds in sludge by activating peroxymonosulfate using dielectric barrier discharge according to claim 1, characterized in that, In step (2), use a peristaltic pump to pump the sludge flowing out of the reactor back to the reaction device.

7. The method for removing perfluorinated compounds in sludge by activating peroxymonosulfate using dielectric barrier discharge according to claim 1, characterized in that, In step (2), the output power of the dielectric barrier discharge is 80 W - 120 W.

8. The method for removing perfluorinated compounds in sludge by activating peroxymonosulfate using dielectric barrier discharge according to claim 1, wherein The molar ratio of the peroxymonosulfate to the perfluorinated compound is (4 - 22):

1.

9. The method for removing perfluorinated compounds in sludge by activating peroxymonosulfate using dielectric barrier discharge according to claim 1, characterized in that, In step (2), the treatment time of the dielectric barrier discharge low-temperature plasma is 10 - 180 minutes.

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