A method for rapid treatment of wastewater containing perfluorinated compounds

Abstract

The present application provides a method for treating perfluorinated compound-containing wastewater rapidly. The method comprises the steps of: preparing an oxy-chloride iron adsorbent by pyrolyzing a raw material of ferric chloride; and treating the perfluorinated compound-containing wastewater by one of the following processes: (i) a batch adsorption process: adding the oxy-chloride iron into the perfluorinated compound-containing wastewater, then constant temperature oscillation, and filtration; or (ii) a dynamic adsorption process: flowing the perfluorinated compound-containing wastewater through an adsorption column filled with the oxy-chloride iron adsorbent, to complete the treatment of the perfluorinated compound-containing wastewater. The present application constructs an intrinsic interface micro-electric field on the surface of the oxy-chloride iron, which significantly accelerates the adsorption kinetics of the perfluorinated compound. The method of the present application is suitable for both batch and dynamic adsorption processes, and exhibits excellent adsorption performance in treating perfluorinated compounds, can reach adsorption equilibrium in 10 minutes, the dynamic adsorption rate is 4.3-6.5 times that of commercial adsorbents, and is easy to regenerate with anti-interference, and has a broad application prospect.

Description

TECHNICAL FIELD

[0001] The application relates to a method for rapidly treating wastewater containing perfluorinated compounds and belongs to the technical field of wastewater treatment. BACKGROUND

[0002] Perfluorinated compounds (PFASs) are ionizable organic chemicals containing multiple C-F bonds, which are artificial organic fluorinated compounds, and the hydrogen atoms on the alkyl chain are replaced by fluorine atoms. Due to its unique chemical and physical properties, such as hydrophobicity, oleophobicity and extraordinary chemical stability, PFASs are widely used as surfactants, flame retardants, lubricants, wetting agents and polymer additives. In the process of industrial production and application, a large amount of perfluorinated compounds are leaked into the aquatic system. In particular, perfluorooctanoic acid (PFOA) is detected in groundwater and surface water. PFASs have environmental persistence and bioaccumulation, which seriously threaten the safety of drinking water of people.

[0003] Recent studies have shown that long-term exposure of people to PFASs contaminated environment, even at very low concentrations, can cause a series of diseases, such as inducing liver poisoning, developmental toxicity, immunotoxicity and even cancer. PFASs also exhibit reproductive toxicity and developmental toxicity, which greatly affect the growth and development of newborns. Based on this, many countries have introduced relevant regulations to limit the production and use of PFASs. In 2016, the United States Environmental Protection Agency (USEPA) set the standard limit of the total amount of perfluorooctanoic acid (PFOA) and perfluorooctyl sulfonic acid (PFOS) in drinking water to 70 ng / L.

[0004] Both traditional biodegradation and chemical degradation have little effect on PFASs removal. Adsorption method has been proved to be one of the most effective methods for removing PFASs in water due to its low energy cost and simple operation. Activated carbon and ion exchange resin are the most widely used adsorbents. For example, Chinese patent document CN106732379A provides a sludge-based activated carbon with high adsorption efficiency for PFOS and PFOA, and its preparation method and application. The sludge-based activated carbon is prepared by drying, activation, high-temperature carbonization treatment, acid leaching, washing and drying. The sludge-based activated carbon is used as an adsorbent in wastewater containing PFOS and PFOA. Chinese patent document CN111171199A discloses an adsorption resin for removing PFASs in water. The resin uses styrene and divinylbenzene as a skeleton material, and selects a suitable pore former and dispersant to prepare a macroporous resin with a moderate pore size. XDC is used as a post-crosslinking agent to undergo alkylation reaction under low steric hindrance. However, the kinetics of the above adsorbents is very slow, and the adsorption method based on these adsorbents generally has the disadvantages of long operation period and low adsorption equipment efficiency. PFAS molecules in water are mostly negatively charged, and the application of an electric field can improve the adsorption rate. For example, electric adsorption. However, such technology requires additional equipment and is difficult to apply on a large scale.

[0005] Therefore, it is of great environmental significance to develop an efficient and rapid adsorption method for treating wastewater containing PFASs. SUMMARY

[0006] In view of the deficiencies of the prior art, the present application provides a method for rapidly treating wastewater containing PFASs. The method of the present application can achieve rapid adsorption of PFASs by electric field driving without the aid of external equipment, and the core adsorbent has the advantages of easy preparation, reproducibility and low cost. At the same time, the method of the present application is applicable to both intermittent and dynamic adsorption processes, and can achieve high-throughput and large-batch treatment of PFAS-containing wastewater, and is superior to activated carbon and ion exchange resin in terms of adsorption rate and treatment capacity.

[0007] The present application is achieved by the following technical solutions:

[0008] A method for rapidly treating wastewater containing PFASs, comprising the following steps:

[0009] (1) preparing an oxyferric chloride adsorbent by heating and cracking ferric chloride raw materials;

[0010] (2) applying the oxyferric chloride as a core adsorbent to one of the following processes for treating wastewater containing PFASs:

[0011] (i) intermittent adsorption process: the oxy-chloride iron is added into the perfluorinated compound-containing wastewater, then constant temperature oscillation, filtration, and the treatment of perfluorinated compound-containing wastewater is completed; or,

[0012] (ii) dynamic adsorption process: the perfluorinated compound-containing wastewater flows through the adsorption column filled with oxy-chloride iron adsorbent, and the treatment of perfluorinated compound-containing wastewater is completed.

[0013] According to the application, preferably, the iron chloride raw material in step (1) is ferric chloride hexahydrate or anhydrous ferric chloride.

[0014] According to the application, preferably, the temperature of the heating and cracking in step (1) is 200-250℃, and the time of the heating and cracking is 0.5-1.5h.

[0015] According to the application, preferably, the iron chloride raw material in step (1) further comprises a grinding step before the heating and cracking.

[0016] According to the application, preferably, the iron chloride raw material in step (1) further comprises a post-treatment step after the heating and cracking, specifically as follows: the product obtained by heating and cracking is naturally cooled to room temperature, then washed and dried to obtain the oxy-chloride iron adsorbent; the washing is sequentially using water, ethanol and acetone for 3-7 times; the drying is drying at 80-100℃ until constant weight.

[0017] According to the application, preferably, the perfluorinated compound in step (2) is perfluorocarboxylic acid or perfluorosulfonic acid; further preferably, the perfluorinated compound is perfluorooctanoic acid, perfluorobutyric acid, perfluoropentanoic acid, perfluorohexanoic acid, perfluoroheptanoic acid or perfluorooctyl sulfonic acid.

[0018] According to the application, preferably, in the intermittent adsorption process of step (2)(i), the concentration of perfluorinated compound in the perfluorinated compound-containing wastewater is 0.1-100mg / L.

[0019] According to the application, preferably, in the intermittent adsorption process of step (2)(i), the ratio of the mass of the oxy-chloride iron to the volume of the perfluorinated compound-containing wastewater is 0.1-1g:1L; the temperature of the constant temperature oscillation is 10-30℃, and the oscillation time is 10-20min.

[0020] According to the application, preferably, in the intermittent adsorption process of (i) of step (2), the oxy-chloride iron adsorbent with adsorbed perfluorinated compounds is recovered and reused after filtration; the regeneration process is as follows: the filtered oxy-chloride iron adsorbent with adsorbed perfluorinated compounds is dried and then soaked in a mixed solution of methanol and sodium chloride aqueous solution for 3-5 hours, and then filtered and dried; the concentration of the sodium chloride aqueous solution is 0.5 mol / L, and the volume ratio of methanol to the sodium chloride aqueous solution in the mixed solution is 1:1; the mass ratio of the dried oxy-chloride iron adsorbent with adsorbed perfluorinated compounds to the volume of the mixed solution is 1 g:100-200 mL.

[0021] According to the application, preferably, in the dynamic adsorption process of (ii) of step (2), the concentration of perfluorinated compounds in the perfluorinated compound-containing wastewater is 0.1-10 μg / L, and more preferably 0.5-5 μg / L.

[0022] According to the application, preferably, in the dynamic adsorption process of (ii) of step (2), the ratio of the loading amount of the oxy-chloride iron adsorbent in the adsorption column to the bed volume of the adsorption column is 0.1-5 g:0.36 cm 3 ; the adsorption column used in the application is a small plastic adsorption column with a height of 2 cm, a diameter of 0.476 cm, and a bed volume of 0.36 cm 3 .

[0023] According to the application, preferably, in the dynamic adsorption process of (ii) of step (2), the flow rate of the perfluorinated compound-containing wastewater is 10-20 mL / min; the perfluorinated compound-containing wastewater flows into the upper end of the adsorption column and flows out of the lower end under the action of a peristaltic pump.

[0024] According to the application, in the dynamic adsorption process of (ii) of step (2), the adsorption of perfluorinated compounds is completed as soon as the perfluorinated compound-containing wastewater passes through the adsorption column, and the water flowing out of the lower end of the adsorption column meets the standard (the concentration of perfluorooctanoic acid in the water is less than 70 ng / L); as the adsorption column is used, the concentration of perfluorooctanoic acid in the water flowing out of the lower end of the adsorption column becomes higher and higher, until the adsorption is ended when the concentration of perfluorooctanoic acid reaches 70 ng / L (the specified value).

[0025] From the chemical principle, the application utilizes the interface micro-electric field of the oxy-chloride iron adsorbent to achieve rapid adsorption. The unique coordination structure of the oxy-chloride iron causes excessive dissolution of anions under hydration, forming a positive interface micro-electric field at the liquid-solid phase interface, and then driving the rapid diffusion of perfluorinated compound anions through the potential difference. The mechanism is generated both relying on the coordination structure of the oxy-chloride iron and combining with the ionization characteristics of short-chain perfluorinated compounds. Through a large number of experiments and theoretical analysis, the applicability of the method in the intermittent adsorption and dynamic adsorption processes is determined.

[0026] The technical features and beneficial effects of the application are as follows:

[0027] 1、The present application utilizes the interface micro-electric field of oxychloride iron to provide electric drive for the mass transfer process of perfluorinated compounds to improve the slow adsorption rate, significantly improve the adsorption treatment efficiency of perfluorinated compounds in wastewater, and compared with other adsorption enhancement methods, no additional equipment and energy injection are needed, greatly reducing the cost.

[0028] 2、The core adsorbent for treating perfluorinated compound-containing wastewater in the present application is composed of oxychloride iron, which is prepared by thermal decomposition method using ferric chloride as raw material, and the preparation process is simple, the experimental equipment requirement is low, and large-scale macro-preparation can be realized, easy to industrialized expansion production, and the material itself has the characteristics of good environmental compatibility, in line with the concept of green chemistry, short-chain perfluorinated compounds are often more difficult to remove, the oxychloride iron in the present application cooperates to realize the efficient removal of perfluorinated compounds, especially short-chain perfluorinated compounds, through electrostatic interaction force, complexation and halogen bond interaction, especially through the surface micro-electric field property of the adsorbent, realizing the efficient removal of charged organic compounds.

[0029] 3、The treatment method of the present application can complete the removal of perfluorinated compound pollutants within ten minutes through intermittent adsorption, greatly shortening the operation time, and the adsorbent has good stability and can be used repeatedly.

[0030] 4、Taking the legal limit of 70ng / L as the standard, the core adsorbent in the present application can reach a treatment capacity of 130000 bed volumes in the dynamic adsorption process, and can maintain stable operation under high flow rate conditions. The present application realizes the controllability of the breakthrough time of perfluorinated compound-containing wastewater, has the characteristics of simple operation, low cost and green environmental protection, while ensuring efficient adsorption, and has a wide application prospect.

[0031] 5、The substrate cost of perfluorinated compound-containing wastewater is often very complex, the treatment method of the present application can maintain a high removal rate of perfluorinated pollutants in complex water quality, and has high selectivity. DETAILED DESCRIPTION

[0032] Figure 1 Figure 1 is the kinetic curve of intermittent adsorption of oxychloride iron in Example 1.

[0033] Figure 2 Figure 2 is a comparison chart of intermittent adsorption performance of Example 1 and Comparative Example 1.

[0034] Figure 3 Figure 3 is a schematic diagram of the equipment for dynamic adsorption of oxychloride iron in Example 2.

[0035] Figure 4 Figure 4 is the treatment capacity of the dynamic adsorption process of Example 2 and Comparative Examples 1 and 2.

[0036] Figure 5 is the anti-interference performance of the oxy-chloride iron adsorption method in Example 4.

[0037] Figure 6 is the anti-interference performance of the oxy-chloride iron adsorption method in Example 4.

[0038] Figure 7 is the adsorption and removal performance of the oxy-chloride iron on different types of perfluorinated compounds in Example 5. DETAILED DESCRIPTION

[0039] The application is further described below in conjunction with specific examples, but the application is not limited thereto.

[0040] The raw materials used in the examples are all conventional raw materials and can be purchased on the market; the methods are all prior art unless otherwise specified.

[0041] The oxy-chloride iron adsorbent used in the examples is prepared according to the method of Preparation Example 1.

[0042] The adsorption column used in the examples is a small plastic adsorption column with a height of 2 cm, a diameter of 0.476 cm, and a bed volume of 0.36 cm 3 The material of the adsorption column is polymethyl methacrylate.

[0043] Preparation Example 1

[0044] Preparation of oxy-chloride iron adsorbent

[0045] 5 grams of iron trichloride hexahydrate were added to an agate mortar, ground and evenly spread on the bottom of a beaker, and placed in a muffle furnace, and heated to 220℃ at a heating rate of 10℃ / min, and then heated at 220℃ in air for 1h; then naturally cooled to room temperature, and the obtained solid was washed with water, ethanol and acetone for 5 times respectively, and then dried at 90℃ to constant weight, to obtain the oxy-chloride iron adsorbent.

[0046] Example 1

[0047] A method for quickly treating wastewater containing perfluorinated compounds, comprising the following steps:

[0048] 0.075g of oxy-chloride iron adsorbent was added to 150mL of perfluorooctanoic acid aqueous solution with a concentration of 0.5mg / L, and then oscillated at 25℃, the oscillation frequency was 200rpm, filtered, and the treatment of wastewater containing perfluorinated compounds was completed; during the oscillation process, samples were taken at oscillation times of 5, 10, 20, 30, 60 and 120 minutes, filtered through a 0.22μm filter membrane, and then tested by LC-MS / MS, and the specific results are shown in Figure 1

[0049] ​The adsorption performance of typical perfluorinated compounds (PFOA) was tested in the intermittent adsorption process of this embodiment, Figure 1 The kinetic curve of the intermittent adsorption process of oxy-chloride iron was obtained from Figure 1 As can be seen from the above table, oxy-chloride iron showed an ultrafast adsorption rate for PFOA, and the adsorption equilibrium could be reached within 10 minutes, and the removal rate reached 93%.

[0050] Comparative Example 1

[0051] A method for treating wastewater containing perfluorinated compounds is as described in Example 1, except that the adsorbent is replaced by iron oxide, magnetite and hydroxyl iron oxide.

[0052] Figure 2 Example 1 and Comparative Example 1 are compared in terms of intermittent adsorption performance, which shows that the adsorption performance of oxy-chloride iron is better than that of other types of iron oxide adsorbents.

[0053] Example 2

[0054] A method for rapidly treating wastewater containing perfluorinated compounds, comprising the following steps:

[0055] (1) Preparation of an adsorption column filled with oxy-chloride iron adsorbent:

[0056] First, fill the end of the adsorption column with glass fibers (as the lower end), and load 1 g of oxy-chloride iron sample into the adsorption column from the other end, and tap a few times to compact the adsorbent bed.

[0057] (2) Dynamic adsorption process

[0058] A perfluorooctanoic acid solution with a concentration of 1 μg / L is passed through the adsorption column at a flow rate of 15 mL / min from the upper end of the adsorption column by a peristaltic pump, and flows out from the lower end, thereby completing the treatment of wastewater containing perfluorinated compounds. As the adsorption column is used, the concentration of perfluorooctanoic acid in the water flowing out from the lower end becomes higher and higher, and the treatment is stopped when the concentration of perfluorinated compounds in the effluent reaches 70 ng / L. The water treatment amount when the effluent concentration reaches 70 ng / L is used as an index for performance evaluation, and samples are taken at regular intervals, and the kinetic constants are calculated using the Yoon-Nelson model.

[0059] Figure 3 The device schematic diagram for the dynamic adsorption process of oxy-chloride iron is shown in the figure, which comprises a liquid storage tank, a peristaltic pump and an adsorption column connected in sequence by pipelines, and the material of the pipelines is silica gel.

[0060] Comparative Example 2

[0061] A method for treating wastewater containing perfluorinated compounds is as described in Example 2, except that the filler of the adsorption column is replaced by commercial activated carbon F400.

[0062] Comparative Example 3

[0063] A method for treating wastewater containing perfluorinated compounds is as described in Example 2, except that the filler of the adsorption column is replaced by commercial ion exchange resin IRA67.

[0064] Figure 4 For the treatment capacity of the dynamic adsorption process of Example 2 and Comparative Example 2 and Comparative Example 3, the treatment capacity of the adsorption method based on oxychloride of iron is as high as 130,000 bed volumes, which is much better than that of ion exchange resin and activated carbon. Table 1 is the kinetic constant calculated from Example 2, Comparative Example 2 and Comparative Example 3, and the adsorption method of the present application is 4.3-6.5 times that of the commercial adsorbent-based adsorption method.

[0065] Table 1

[0066] Adsorption kinetic rate constant (min -1 )]]> Example 6 0.0013 Comparative Example 2 0.0003 Comparative Example 3 0.0002

[0067] Example 3

[0068] The regeneration performance of the oxychloride of iron adsorption method was tested. The oxychloride of iron adsorbent used in the intermittent adsorption process for adsorbing perfluorinated compounds was dried to constant weight at 60°C, then immersed in a mixed solution of methanol and aqueous sodium chloride solution (methanol and 0.5 mol / L aqueous sodium chloride solution mixed in a volume ratio of 1:1) for 4 hours, and after drying, the mass of the oxychloride of iron adsorbent adsorbing perfluorinated compounds was 1 g and the volume of the mixed solution was 140 mL; then filtered, vacuum dried to constant weight at 60°C, and the regeneration was completed, and then the removal rate of perfluorooctanoic acid was tested.

[0069] Figure 5 For the regeneration performance of the oxychloride of iron adsorbent, it shows that the adsorbent of the present application has good reutilization performance.

[0070] Example 4

[0071] A method for rapidly treating wastewater containing perfluorinated compounds is as described in Example 2, except that humic acid and chloride ions are added to the water storage tank as interferents (both at a concentration of 5 mg / L), and the anti-interference performance of the oxychloride of iron is tested. Figure 6 For the anti-interference performance of the oxychloride of iron adsorption method, the results show that the method of the present application has good anti-interference performance.

[0072] Example 5

[0073] The universality of the adsorption performance of the oxychloride of iron was tested. The types of pollutants in Example 1 were replaced by perfluorobutyric acid, perfluoropentanoic acid, perfluorohexanoic acid and perfluoroheptanoic acid, and then the intermittent adsorption performance was tested.

[0074] Figure 7The adsorption performance of the iron oxychloride to other kinds of perfluorinated compound pollutants is good, and various perfluorinated pollutants are removed well, which indicates that the method has good universality.

Claims

1. A method for rapidly treating wastewater containing perfluorinated compounds, comprising the following steps: (1) Prepare oxy-based ferric chloride adsorbent by heating and pyrolyzing ferric chloride raw material; the heating and pyrolyzing temperature is 200-250℃ and the heating and pyrolyzing time is 0.5-1.5h; (2) The oxy-containing ferric chloride is used as the core adsorbent in one of the following processes to treat wastewater containing perfluorinated compounds: the perfluorinated compounds are perfluorocarboxylic acids or perfluorosulfonic acids; (i) Intermittent adsorption process: Ferric chloride is added to wastewater containing perfluorinated compounds, followed by constant temperature shaking and filtration to complete the treatment of the wastewater containing perfluorinated compounds; the concentration of perfluorinated compounds in the wastewater is 0.1-100 mg / L; the mass ratio of ferric chloride added to the volume of wastewater containing perfluorinated compounds is 0.1-1 g:1 L; or, (ii) Dynamic adsorption process: Wastewater containing perfluorinated compounds is passed through an adsorption column packed with ferric chloride adsorbent to treat the wastewater; the concentration of perfluorinated compounds in the wastewater is 0.1-10 μg / L; the ratio of the amount of ferric chloride adsorbent loaded in the adsorption column to the bed volume of the adsorption column is 0.1-5 g:0.36 cm³. 3 .

2. The method for rapidly treating wastewater containing perfluorinated compounds according to claim 1, characterized in that, The ferric chloride raw material mentioned in step (1) is ferric chloride hexahydrate or anhydrous ferric chloride.

3. The method for rapidly treating wastewater containing perfluorinated compounds according to claim 1, characterized in that, The ferric chloride raw material mentioned in step (1) also includes a grinding step before heating and cracking; The ferric chloride raw material, after being heated and pyrolyzed, also includes a post-processing step, as follows: the product obtained from the heated pyrolysis is naturally cooled to room temperature, washed, and dried to obtain the oxy-based ferric chloride adsorbent; the washing is performed by washing with water, ethanol, and acetone 3-7 times each; the drying is performed at 80-100℃ to constant weight.

4. The method for rapidly treating wastewater containing perfluorinated compounds according to claim 1, characterized in that, The perfluorinated compound mentioned in step (2) is perfluorooctanoic acid, perfluorobutyric acid, perfluorovalerate, perfluorohexanoic acid, perfluoroheptanoic acid, or perfluorooctylsulfonic acid.

5. The method for rapidly treating wastewater containing perfluorinated compounds according to claim 1, characterized in that, In step (2) (i) of the intermittent adsorption process, the temperature of the isothermal oscillation is 10-30℃ and the oscillation time is 10-20min.

6. The method for rapidly treating wastewater containing perfluorinated compounds according to claim 1, characterized in that, In step (2) (i) of the intermittent adsorption process, the oxygen-based ferric chloride adsorbent adsorbed with perfluorinated compounds obtained by filtration is recovered and regenerated for reuse. The regeneration step is as follows: the oxygen-based ferric chloride adsorbent adsorbed with perfluorinated compounds obtained by filtration is dried and then soaked in a mixed solution of methanol and sodium chloride aqueous solution for 3-5 hours, followed by filtration and drying. The concentration of the sodium chloride aqueous solution is 0.5 mol / L, and the volume ratio of methanol and sodium chloride aqueous solution in the mixed solution is 1:

1. The mass ratio of the oxygen-based ferric chloride adsorbent adsorbed with perfluorinated compounds after drying to the volume ratio of the mixed solution is 1 g: 100-200 mL.

7. The method for rapidly treating wastewater containing perfluorinated compounds according to claim 1, characterized in that, In step (2) (ii) dynamic adsorption process, the concentration of perfluorinated compounds in the wastewater containing perfluorinated compounds is 0.5-5 μg / L.

8. The method for rapidly treating wastewater containing perfluorinated compounds according to claim 1, characterized in that, In step (2) (ii) of the dynamic adsorption process, the flow rate of the perfluorinated wastewater is 10-20 mL / min; the perfluorinated wastewater flows in from the upper end of the adsorption column and flows out from the lower end through the action of a peristaltic pump.

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