Method for removing perfluorinated compounds in water by using superfine powdered activated carbon

Abstract

The invention relates to the technical field of water treatment, in particular to a method for removing perfluorinated compounds in water by using superfine powdered activated carbon. The method comprises the following steps: adding activated carbon slurry into a to-be-treated water sample containing a perfluorinated compound, and carrying out first stirring treatment to obtain a first mixed solution; adding a coagulant into the first mixed solution, and carrying out second stirring treatment to obtain a second mixed solution; adding a flocculating agent into the second mixed solution, and carrying out third stirring treatment to obtain a third mixed solution; and removing the precipitate in the third mixed solution so as to realize the removal of the perfluorinated compound in the water sample to be treated. Wherein activated carbon adopted in the activated carbon slurry is superfine powder activated carbon, and the superfine powder activated carbon has the median particle size of 1-5 [mu] m, the specific surface area of 900-1500 m < 2 > / g, the average pore size of 1.5-2.0 nm and the total pore volume of 0.4-0.8 mL / g. The method can solve the problems that perfluorinated compounds are difficult to remove, the adsorption capacity of conventional activated carbon is limited, the cost of additional structures is high and the like in the existing tap water, sewage and wastewater treatment process, provides a solution for treatment of perfluorinated compounds in drinking water, domestic sewage and industrial wastewater, and has a good practical application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of water treatment, and particularly relates to a method for removing perfluorinated compounds in water using ultra-fine powdered activated carbon. Background Art

[0002] Perfluorinated compounds are a new type of persistent organic compound that does not exist in nature and is synthetically produced. All hydrogen atoms connected to carbon atoms in its molecule are replaced by fluorine atoms and are connected to various hydrophilic groups such as carboxyl groups and sulfonic acid groups. Perfluorinated compounds have various excellent properties such as hydrophobicity, oil repellency, high temperature resistance, and significantly reducing the surface tension of water, and are widely used in various industries. However, perfluorinated compounds have extremely high stability, and conventional solar illumination, chemical reactions, and microbial metabolism in nature cannot degrade them. Moreover, perfluorinated compounds can exist in organisms for a long time, causing many adverse effects on organisms such as reproductive toxicity, endocrine disruption toxicity, liver toxicity, and immunotoxicity. Currently, perfluorooctanoic acid and perfluorooctane sulfonic acid have been classified as Class 1 and Class 2B carcinogens by IARC.

[0003] The extensive use has inevitably led to the entry of perfluorinated compounds into the water environment through various channels, and major river and lake waters are threatened by perfluorinated compound pollution. Although perfluorinated compounds usually exist in water at extremely low concentrations, they can enter the water source through runoff. The original design of conventional water treatment plants only targets particulate matter and pathogenic microorganisms, and the removal effect on perfluorinated compounds is very limited. Therefore, most perfluorinated compounds will enter the treated water and tap water and be ingested by the human body through the drinking water exposure route. At the same time, in April 2023, the new version of the "Hygienic Standard for Drinking Water" (GB5749-2022) was officially implemented, incorporating perfluorooctanoic acid and perfluorooctane sulfonic acid into the appendix, with the specified limits being 80 ng / L and 40 ng / L respectively, which have brought new requirements and challenges to the drinking water industry in controlling the pollution risk of perfluorinated compounds.

[0004] Activated carbon adsorption is currently an effective and feasible method for removing perfluorinated compounds in drinking water. However, the granular activated carbon or activated carbon used in the existing processes of water treatment plants has a relatively large particle size, and its adsorption capacity cannot be fully exerted within the limited contact time in the plant, resulting in a very limited adsorption effect on perfluorinated compounds. Therefore, upgrading the existing activated carbon adsorption technology in water treatment plants to improve the removal effect on perfluorinated compounds has significant practical significance. Summary of the Invention

[0005] The present invention aims to solve at least one of the technical problems in the related art to a certain extent. To this end, the present invention provides a method for removing perfluorinated compounds in water using ultrafine powdered activated carbon. The method adopts ultrafine powdered activated carbon and its supporting enhanced coagulation and precipitation process to effectively remove perfluorinated compounds in water. The enhanced coagulation process using a polymer flocculant can efficiently settle and separate the ultrafine powdered activated carbon added to the water, further improve the removal effect of perfluorinated compounds, avoid the additional impact brought by the ultrafine powdered activated carbon, reduce the concentration of perfluorinated compounds in the effluent, and ensure that the effluent quality of waterworks, domestic sewage treatment plants, industrial wastewater treatment plants, and reclaimed water plants meets the relevant requirements.

[0006] To this end, in the first aspect of the present invention, a method for removing perfluorinated compounds in water using ultrafine powdered activated carbon is provided. The method includes the following steps:

[0007] Adding activated carbon slurry to the water sample to be treated containing perfluorinated compounds, and performing a first stirring treatment to obtain a first mixed solution;

[0008] Adding a coagulant to the first mixed solution and performing a second stirring treatment to obtain a second mixed solution;

[0009] Adding a flocculant to the second mixed solution and performing a third stirring treatment to obtain a third mixed solution;

[0010] Removing the precipitate in the third mixed solution, thereby achieving the removal of perfluorinated compounds in the water sample to be treated;

[0011] Among them, the activated carbon used in the activated carbon slurry is ultrafine powdered activated carbon. The median particle size of the ultrafine powdered activated carbon is 1 μm - 5 μm, the specific surface area is 900 m 2 / g - 1500 m 2 / g, the average pore diameter is 1.5 nm - 2.0 nm, and the total pore volume is 0.4 mL / g - 0.8 mL / g.

[0012] The method provided by the present invention adsorbs perfluorinated compounds in water by using pre-processed ultrafine powdered activated carbon with a median particle size less than 5 μm, and at the same time cooperates with the enhanced coagulation process of combining a coagulant and a flocculant to efficiently separate the ultrafine powdered activated carbon adsorbed with perfluorinated compounds from the water, avoiding the impact on the original process of the waterworks by the ultrafine powdered activated carbon; at the same time, the ultrafine powdered activated carbon used in this method is transported in the form of pre-processed carbon slurry and added to the waterworks, avoiding the potential dust explosion hazard that may be brought during the production, transportation, and use of the ultrafine powdered activated carbon, and reducing the environmental pollution problem of worker operation; in addition, the flocculant selected by the present invention can further remove perfluorinated compounds through electrostatic action, fully ensuring water quality safety.

[0013] According to an embodiment of the present invention, the content of the ultrafine powdered activated carbon in the activated carbon slurry is 10 wt% - 30 wt%.

[0014] According to an embodiment of the present invention, the content of the ultrafine powdered activated carbon in the first mixed liquid is 5 mg / L - 40 mg / L.

[0015] According to an embodiment of the present invention, the content of the coagulant in the second mixed liquid is 5 mg / L - 20 mg / L.

[0016] According to an embodiment of the present invention, the coagulant includes at least one of polyaluminum chloride, aluminum sulfate, ferric trichloride, and polyferric sulfate.

[0017] According to an embodiment of the present invention, the content of elemental aluminum or elemental iron in the coagulant is ≥ 10 wt%.

[0018] According to an embodiment of the present invention, the content of the flocculant in the third mixed liquid is 0.1 mg / L - 1 mg / L.

[0019] According to an embodiment of the present invention, the flocculant includes a cationic flocculant.

[0020] According to an embodiment of the present invention, the cationic flocculant includes at least one of cationic polyacrylamide and poly(dimethyldiallylammonium chloride).

[0021] According to an embodiment of the present invention, the perfluorinated compound includes at least one of perfluoroalkyl acids and perfluoroalkyl sulfonic acids.

[0022] According to an embodiment of the present invention, the perfluoroalkyl acid includes at least one of perfluorobutyric acid, perfluorovaleric acid, perfluorohexanoic acid, perfluoroheptanoic acid, perfluorooctanoic acid, perfluorononanoic acid, and perfluorodecanoic acid.

[0023] According to an embodiment of the present invention, the perfluoroalkyl sulfonic acid includes at least one of perfluorobutyl sulfonic acid, perfluorohexyl sulfonic acid, perfluorooctyl sulfonic acid, and perfluorodecyl sulfonic acid.

[0024] According to an embodiment of the present invention, the time of the first stirring treatment is 5 min - 30 min.

[0025] According to an embodiment of the present invention, the stirring intensity of the first stirring treatment is 600 / s - 1000 / s in terms of hydraulic gradient.

[0026] According to an embodiment of the present invention, the time of the second stirring treatment is 10 s - 60 s.

[0027] According to an embodiment of the present invention, the stirring intensity of the second stirring treatment is 600 / s - 1000 / s in terms of hydraulic gradient.

[0028] According to an embodiment of the present invention, the time of the third stirring treatment is 10 min - 30 min.

[0029] According to an embodiment of the present invention, the stirring intensity of the third stirring treatment is 30 / s - 60 / s in terms of hydraulic gradient.

[0030] According to an embodiment of the present invention, the method further comprises:

[0031] Adding a pH regulator to the water sample to be treated containing perfluorinated compounds to adjust the pH value of the water sample to be treated to 6.0 - 7.5.

[0032] According to an embodiment of the present invention, the pH regulator comprises an acidic regulator and / or a basic regulator.

[0033] According to an embodiment of the present invention, the acidic regulator comprises at least one of sulfuric acid, hydrochloric acid, nitric acid, and carbon dioxide.

[0034] According to an embodiment of the present invention, the basic regulator comprises at least one of sodium hydroxide, lime, and sodium carbonate.

[0035] According to an embodiment of the present invention, the step of removing the precipitate in the third mixture comprises:

[0036] Performing a precipitation treatment on the third mixture until the turbidity of the supernatant < 1 NTU;

[0037] Performing a filtration treatment on the supernatant until the turbidity of the filtrate < 0.3 NTU.

[0038] According to an embodiment of the present invention, the time of the precipitation treatment is 30 min - 120 min.

[0039] According to an embodiment of the present invention, the method further comprises:

[0040] Performing a filtration treatment on the supernatant until the turbidity of the filtrate < 0.3 NTU, and adjusting the pH value of the filtrate to 6.5 - 8.5.

[0041] Advantages of the present invention over the prior art:

[0042] (1) The method provided by the present invention uses ultra-fine powdered activated carbon with a smaller particle size, which has a better removal effect on perfluorinated compounds. However, the ultra-fine powdered activated carbon itself is not easily removed in water and will cause secondary pollution. By combining specific coagulants and flocculants and adopting specific steps and process parameters, the present invention achieves a better overall interaction, can efficiently remove the ultra-fine powdered activated carbon, avoids the secondary pollution problem caused by the use of ultra-fine powdered activated carbon, and reduces the interference with the existing processes of water treatment plants, domestic sewage treatment plants, industrial wastewater treatment plants, and reclaimed water treatment plants. In addition, the flocculant selected by the present invention can further remove perfluorinated compounds and improve the water treatment efficiency;

[0043] (2) The ultra-fine powdered activated carbon used in the present invention is transported in the form of pre-processed carbon slurry and added to the water treatment plant, avoiding the potential dust explosion hazard during the production, transportation, and use of the ultra-fine powdered activated carbon and reducing the environmental pollution problem of the workers' operation;

[0044] (3) The method provided by the present invention is simple and convenient, without the need to add additional structures in the water treatment plant, and the usage method, frequency, and scale are flexible and convenient, with a limited impact on the drinking water treatment cost. It solves the perfluorinated compound pollution problem faced by water treatment plants, domestic sewage treatment plants, industrial wastewater treatment plants, and reclaimed water treatment plants without causing additional impacts, and has good economic efficiency and practical application prospects.

[0045] The additional aspects and advantages of the present invention will be partially given in the following description, partially become obvious from the following description, or be understood through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The above and / or additional aspects and advantages of the present invention will become obvious and easy to understand from the description of the embodiments in conjunction with the following drawings, where:

[0047] Figure 1 Shows the particle size distribution diagram of the ultra-fine powdered activated carbon in the activated carbon slurry used in Example 1 of the present invention;

[0048] Figure 2 Shows the micropore distribution diagram of the ultra-fine powdered activated carbon in the activated carbon slurry used in Example 1 of the present invention;

[0049] Figure 3 Shows the adsorption effect diagram of the ultra-fine powdered activated carbon in the activated carbon slurry used in Example 1 of the present invention on perfluoroalkyl acids;

[0050] Figure 4 Shows the adsorption effect diagram of the ultra-fine powdered activated carbon in the activated carbon slurry used in Example 1 of the present invention on perfluoroalkyl sulfonic acids. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0051] Embodiments of the present invention will be described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as a limitation of the present invention.

[0052] It should be noted that the terms "first" and "second" are only used for descriptive purposes and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of such features. Further, in the description of the present invention, unless otherwise stated, the meaning of "a plurality" is two or more.

[0053] In the ranges disclosed herein, the endpoints and any values are not limited to the exact range or value, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0054] To make the present invention easier to understand, certain technical and scientific terms are specifically defined below. Unless otherwise clearly defined elsewhere in this document, all other technical and scientific terms used herein have the meanings commonly understood by those of ordinary skill in the art to which the present invention pertains.

[0055] In this document, the term "comprising" or "including" is an open expression, that is, it includes the content specified by the present invention, but does not exclude other aspects.

[0056] In this document, the terms "optionally", "optional" or "option" generally mean that the subsequent events or conditions may or may not occur, and this description includes the cases where such events or conditions occur, as well as the cases where such events or conditions do not occur.

[0057] According to an embodiment of the present invention, a first aspect of the present invention provides a method for removing perfluorinated compounds in water using ultrafine powder activated carbon, the method comprising the following steps:

[0058] (1) Adding activated carbon slurry to the water sample to be treated containing perfluorinated compounds, and performing a first stirring treatment to obtain a first mixed solution;

[0059] Wherein, the activated carbon used in the activated carbon slurry is ultrafine powder activated carbon, the median particle size of the ultrafine powder activated carbon is 1 μm - 5 μm, the specific surface area is 900 m 2 / g - 1500 m 2 / g, the average pore diameter is 1.5 nm - 2.0 nm, and the total pore volume is 0.4 mL / g - 0.8 mL / g.

[0060] In the method provided by the present invention, the ultra-fine powdered activated carbon adopted has a relatively small particle size and can effectively remove perfluorinated compounds within a short contact time in a water treatment plant. At the same time, aiming at the problems of potential operating environmental pollution and dust explosion risk brought by the ultra-fine powdered activated carbon itself, it is proposed to produce, transport and use the ultra-fine powdered activated carbon in the form of carbon slurry, ensuring the safety of the whole process.

[0061] According to a specific embodiment of the present invention, the content of the ultra-fine powdered activated carbon in the activated carbon slurry is 10wt%-30wt%. As some specific examples, the content of the ultra-fine powdered activated carbon in the activated carbon slurry can be 10wt%, 20wt%, 30wt%, etc. Specifically, commercially available conventional activated carbon can be processed into ultra-fine powdered activated carbon with a median particle size of less than 5μm by wet grinding. Without drying and bagging, it can be directly formulated into a carbon slurry with a content of 10wt%-30wt%, transported to a water treatment plant by containers such as tank trucks and ton barrels, stored in a storage tank for standby, and quantitatively added by a metering pump when needed, avoiding the safety hazards existing in dry grinding, drying after conventional wet grinding and adding ultra-fine powdered activated carbon.

[0062] According to a specific embodiment of the present invention, the content of the ultra-fine powdered activated carbon in the first mixed liquid is 5mg / L-40mg / L. As some specific examples, the content of the ultra-fine powdered activated carbon in the first mixed liquid can be 5mg / L, 10mg / L, 20mg / L, 40mg / L, etc.

[0063] According to a specific embodiment of the present invention, the types of the perfluorinated compounds are not particularly limited. As some specific examples, the perfluorinated compounds include at least one of perfluoroalkyl acids and perfluoroalkyl sulfonic acids.

[0064] According to a specific embodiment of the present invention, the types of the perfluoroalkyl acids are not particularly limited. As some specific examples, the perfluoroalkyl acids include at least one of perfluorobutyric acid (PFBA), perfluoropentanoic acid (PFPeA), perfluorohexanoic acid (PFHxA), perfluoroheptanoic acid (PFHpA), perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), and perfluorodecanoic acid (PFDA).

[0065] According to a specific embodiment of the present invention, the types of the perfluoroalkyl sulfonic acids are not particularly limited. As some specific examples, the perfluoroalkyl sulfonic acids include at least one of perfluorobutyl sulfonic acid (PFBS), perfluorohexyl sulfonic acid (PFHxS), perfluorooctyl sulfonic acid (PFOS), and perfluorodecyl sulfonic acid (PFDS).

[0066] According to specific embodiments of the present invention, the time of the first stirring treatment is 5 min - 30 min. As some specific examples, the time of the first stirring treatment can be 5 min, 10 min, 20 min, 30 min, etc.

[0067] According to specific embodiments of the present invention, the stirring intensity of the first stirring treatment is 600 / s - 1000 / s in terms of hydraulic gradient. As some specific examples, the stirring intensity of the first stirring treatment in terms of hydraulic gradient (G value) can be 600 / s, 700 / s, 800 / s, 900 / s, 1000 / s, etc.

[0068] According to specific embodiments of the present invention, the method further includes:

[0069] Adding a pH regulator to the water sample to be treated containing perfluorinated compounds to adjust the pH value of the water sample to be treated to 6.0 - 7.5.

[0070] According to specific embodiments of the present invention, the pH regulator includes an acidic regulator and / or a basic regulator.

[0071] According to specific embodiments of the present invention, the type of the acidic regulator is not particularly limited. As some specific examples, the acidic regulator includes at least one of sulfuric acid, hydrochloric acid, nitric acid, and carbon dioxide.

[0072] According to specific embodiments of the present invention, the type of the basic regulator is not particularly limited. As some specific examples, the basic regulator includes at least one of sodium hydroxide, lime, and sodium carbonate.

[0073] (2) Adding a coagulant to the first mixed solution and performing a second stirring treatment to obtain a second mixed solution.

[0074] According to specific embodiments of the present invention, the content of the coagulant in the second mixed solution is 5 mg / L - 20 mg / L. As some specific examples, the content of the coagulant in the second mixed solution can be 5 mg / L, 10 mg / L, 15 mg / L, 20 mg / L, etc.

[0075] According to specific embodiments of the present invention, the type of the coagulant is not particularly limited. As some specific examples, the coagulant includes at least one of polyaluminum chloride, aluminum sulfate, ferric trichloride, and polyferric sulfate.

[0076] According to specific embodiments of the present invention, the content of elemental aluminum or elemental iron in the coagulant is ≥10 wt%.

[0077] According to specific embodiments of the present invention, the time of the second stirring treatment is 10 s - 60 s. As some specific examples, the time of the second stirring treatment can be 10 s, 20 s, 30 s, 40 s, 50 s, 60 s, etc.

[0078] According to specific embodiments of the present invention, the stirring intensity of the second stirring treatment is 600 / s - 1000 / s in terms of hydraulic gradient. As some specific examples, the stirring intensity of the second stirring treatment in terms of hydraulic gradient (G value) can be 600 / s, 700 / s, 800 / s, 900 / s, 1000 / s, etc.

[0079] (3) Add a flocculant to the second mixed solution and perform a third stirring treatment to obtain a third mixed solution.

[0080] Aiming at the problem that the ultra-fine powder activated carbon is difficult to remove due to its small particle size, on the basis of the original coagulation process in the water plant, the coagulant is combined with a polymer flocculant to strengthen the coagulation effect, so that the adsorbed ultra-fine powder activated carbon is completely removed and separated from the water, avoiding the additional impact of the use of ultra-fine powder activated carbon on the water treatment process of the water plant, ensuring that the turbidity of the effluent meets the standard, and at the same time further complexing and removing perfluorinated compounds by using the characteristics of the coagulation process, obtaining a perfect process flow suitable for water plants, domestic sewage treatment plants, industrial wastewater treatment plants, and reclaimed water plants.

[0081] According to specific embodiments of the present invention, the content of the flocculant in the third mixed solution is 0.1 mg / L - 1 mg / L. As some specific examples, the content of the flocculant in the third mixed solution can be 0.1 mg / L, 0.2 mg / L, 0.4 mg / L, 0.6 mg / L, 0.8 mg / L, 1 mg / L, etc.

[0082] According to specific embodiments of the present invention, the flocculant includes a cationic flocculant.

[0083] According to specific embodiments of the present invention, the type of the cationic flocculant is not particularly limited. As some specific examples, the cationic flocculant includes at least one of cationic polyacrylamide and poly(dimethyldiallylammonium chloride).

[0084] According to specific embodiments of the present invention, the time of the third stirring treatment is 10 min - 30 min. As some specific examples, the time of the third stirring treatment can be 10 min, 15 min, 20 min, 30 min, etc.

[0085] According to specific embodiments of the present invention, the stirring intensity of the third stirring treatment is 30 / s - 60 / s in terms of hydraulic gradient. As some specific examples, the stirring intensity of the third stirring treatment in terms of hydraulic gradient can be 30 / s, 40 / s, 50 / s, 60 / s, etc. Specifically, the third stirring treatment needs to be slowly stirred at a relatively small G value, otherwise the flocs formed by the flocculant will be broken up.

[0086] Specifically, the specific operation of step (3) can be: adding a flocculant to the second mixed solution, and stirring for 5 minutes respectively under the conditions of G values of 60 / s, 50 / s, and 30 / s to obtain a third mixed solution.

[0087] (4) Removing the precipitate in the third mixed solution, thereby achieving the removal of perfluorinated compounds in the water sample to be treated.

[0088] According to specific embodiments of the present invention, the step of removing the precipitate in the third mixed solution includes:

[0089] ① Performing precipitation treatment on the third mixed solution until the turbidity of the supernatant < 1 NTU.

[0090] Specifically, "NTU" is a standard unit for measuring the turbidity of a solution. Controlling the turbidity of the supernatant < 1 NTU can remove most of the ultrafine powder carbon adsorbed with perfluorinated compounds by precipitation.

[0091] According to specific embodiments of the present invention, the time of the precipitation treatment is 30 min - 120 min. As some specific examples, the time of the precipitation treatment can be 30 min, 60 min, 90 min, 120 min, etc.

[0092] According to specific embodiments of the present invention, the manner of the precipitation treatment is not particularly limited. For example, a sedimentation tank can be used.

[0093] ② Performing filtration treatment on the supernatant until the turbidity of the filtrate < 0.3 NTU.

[0094] According to specific embodiments of the present invention, the manner of the filtration treatment is not particularly limited. For example, a filter tank can be used. The type of filter media in the filter tank is not particularly limited as long as the filtration purpose can be achieved. For example, quartz sand can be used.

[0095] According to specific embodiments of the present invention, the method further includes:

[0096] Performing filtration treatment on the supernatant until the turbidity of the filtrate < 0.3 NTU, and adjusting the pH value of the filtrate to 6.5 - 8.5.

[0097] The solution of the present invention will be explained below in conjunction with embodiments. Those skilled in the art will understand that the following embodiments are only used to illustrate the present invention and should not be construed as limiting the scope of the present invention. For those without specific techniques or conditions noted in the embodiments, the techniques or conditions described in the literature in the art or according to the product specifications are followed. Reagents or instruments without the manufacturer noted are all conventional products that can be obtained through commercial purchase.

[0098] Example 1

[0099] This example explored the removal effect of ultrafine powdered activated carbon on perfluorinated compounds in water. The specific steps are as follows:

[0100] 11 perfluorinated compound (perfluorobutyric acid PFBA, perfluoropentanoic acid PFPeA, perfluorohexanoic acid PFHxA, perfluoroheptanoic acid PFHpA, perfluorooctanoic acid PFOA, perfluorononanoic acid PFNA, perfluorodecanoic acid PFDA, perfluorobutanesulfonic acid PFBS, perfluorohexanesulfonic acid PFHxS, perfluorooctanesulfonic acid PFOS, perfluorodecanesulfonic acid PFDS) standards and a phosphate buffer solution with pH = 7 were added to ultrapure water so that the concentration of each perfluorinated compound in the ultrapure water was 200 μg / L;

[0101] Activated carbon slurry was added so that the concentration of ultrafine powdered activated carbon in the water was 5 mg / L, and then it was stirred and mixed for 15 min under the condition of G value of 800 / s;

[0102] The particle size distribution diagram of the ultrafine powdered activated carbon is as Figure 1 shown, the micropore distribution diagram is as Figure 2 shown, and the adsorption effect diagrams of the ultrafine powdered activated carbon on perfluoroalkyl acids and perfluoroalkyl sulfonic acids are as Figure 3 and Figure 4 shown.

[0103] The test results show that the ultrafine powdered activated carbon adopted in the present invention has strong adsorption ability for various types of perfluorinated compounds. Adding 5 mg / L of activated carbon can effectively adsorb and remove perfluorinated compounds within 30 min of contact time. In particular, the removal rates of perfluorooctanoic acid and perfluorooctanesulfonic acid included in the appendix of the sanitary standard for domestic drinking water reached 40% and 75% respectively.

[0104] Example 2

[0105] This example provides a method for removing perfluorinated compounds in water. The method includes the following steps:

[0106] Add standard substances of PFOA and PFOS to natural water to make the concentrations of PFOA and PFOS in the water 100 ng / L respectively. Add hydrochloric acid and / or sodium hydroxide to adjust the pH value of the water to 6.0 to obtain raw water. The situation of this natural water is as follows: total organic carbon (TOC) = 2.34 mg / L, UV 254 = 0.044 cm -1 , initial turbidity = 2.36 NTU, initial pH value = 7.6;

[0107] Add activated carbon slurry to make the concentration of ultrafine powdered activated carbon in the water 30 mg / L. Then stir and mix for 15 min under the condition of G value of 800 / s. At this time, the turbidity of the water is 18.90 NTU;

[0108] Add polyaluminum chloride coagulant (its content is 15 mg / L), and quickly stir for 60 s under the condition of G value of 800 / s;

[0109] Add cationic polyacrylamide flocculant (its content is 0.2 mg / L), and slowly stir for 5 min each under the conditions of G values of 60 / s, 50 / s, and 30 / s;

[0110] Take the supernatant after natural sedimentation for 30 min, and then filter it with simulated quartz sand.

[0111] In this example, the effect of removing perfluorinated compounds from water is shown in Table 1:

[0112] Table 1

[0113]

[0114]

[0115] Among them, " / " indicates non-existence or undetected.

[0116] The results show that in natural water samples containing various natural organic matters, the ultrafine powdered activated carbon shows adsorption and removal rates of 56.6% and 59.0% respectively for PFOA or PFOS solutions with a concentration of 100 ng / L. In addition, the enhanced coagulation and sedimentation process using polymer flocculants proposed in the present invention can further remove about 5% of PFOA and PFOS, which indicates that the water treatment method proposed in the present invention can effectively control perfluorinated compounds in source water, and the final concentrations of PFOA and PFOS are reduced to 37.9 and 37.66 ng / L respectively, meeting the specified limit requirements for PFOA and PFOS in the appendix of the new "Hygienic Standards for Drinking Water" (GB 5749-2022) (40 and 80 ng / L respectively).

[0117] In addition, when 30 mg / L of ultrafine powdered activated carbon was added to the natural water sample, its turbidity increased from 2.36 NTU to 18.90 NTU. After being treated by the enhanced coagulation and sedimentation process, the turbidity decreased to 0.07 NTU, approaching the turbidity of ultrapure water, indicating that almost all of the ultrafine powdered activated carbon was separated and removed. At the same time, the UV 254 of the raw water also decreased by 52.3%, which shows that the method provided by the present invention can remove perfluorinated compounds in water without bringing negative impacts such as increased turbidity, and can also remove some organic matters in natural water.

[0118] Example 3

[0119] The difference between this example and Example 2 is only that: the flocculant used is poly(dimethyldiallylammonium chloride).

[0120] The effect of removing perfluorinated compounds in water in this example is shown in Table 2:

[0121] Table 2

[0122]

[0123] After choosing poly(dimethyldiallylammonium chloride) as the flocculant, the removal rates of the typical perfluorinated compounds PFOA and PFOS by the method proposed by the present invention are 63.9% and 57.3% respectively, and the concentrations of PFOA and PFOS in the treated water are both within the limit values specified in the "Sanitary Standards for Drinking Water" (GB5749-2022).

[0124] Example 4

[0125] The difference between this example and Example 2 is only that: the concentrations of PFOA and PFOS in the raw water are 500 ng / L.

[0126] The effect of removing perfluorinated compounds in water in this example is shown in Table 3:

[0127] Table 3

[0128]

[0129] After the concentrations of perfluorinated compounds in the raw water are increased to 500 ng / L, the removal rates of the typical perfluorinated compounds PFOA and PFOS by the method proposed by the present invention are 69.7% and 79.1% respectively. The method proposed by the present invention shows better effects under the condition of higher concentrations of perfluorinated compounds, which indicates that the method provided by the present invention can adapt to different pollution situations and solve the pollution problem of high-concentration perfluorinated compounds in water.

[0130] Example 5

[0131] This example was carried out in a water plant in the eastern region. The pilot-scale equipment in the water plant, that is, the equipment simulating the full process operation of the water plant, was used to test the proposed scheme in this study. The scale of the pilot-scale equipment for treating drinking water is 1 t / h, and the treatment process includes pretreatment, coagulation sedimentation, sand filtration, ozonated activated carbon, and disinfection. The influent is the source water from a reservoir in this region. The treatment includes the following steps:

[0132] In the pretreatment section, ultrafine powdered activated carbon slurry with a mass fraction of 30 wt% was added through a chemical dosing pipeline, so that the concentration of ultrafine powdered activated carbon in the pretreatment tank was 30 mg / L, and it was stirred for 15 min under the condition of G value of 1000 / s;

[0133] In the coagulation sedimentation section, aluminum sulfate and cationic polyacrylamide were successively added to the coagulation mixing tank through the chemical dosing pipeline, so that the concentration of aluminum sulfate in the water was 15 mg / L (stirred for 30 s under the condition of G value of 600 / s), and the concentration of cationic polyacrylamide was 0.2 mg / L (stirred for 5 min respectively under the conditions of G value of 60 / s, 50 / s, and 30 / s);

[0134] Subsequently, it underwent the steps of sand filtration, ozonated activated carbon, and disinfection treatment.

[0135] The initial turbidity of this source water was 8.05 NTU. After adding ultrafine powdered activated carbon in the pretreatment section, the turbidity was 19.64 NTU, and the final effluent turbidity was 0.03 NTU. The turbidity removal rate was 99.6% compared with the raw water and 99.8% compared with the effluent after pretreatment.

[0136] The effect of removing perfluorinated compounds in water in this example is shown in Table 4:

[0137] Table 4

[0138]

[0139]

[0140] Note: N.D. means not detected.

[0141] Under the conditions of simulating the treatment of drinking water in an actual water treatment plant, the method proposed in the present invention shows good removal effects on various types of perfluorinated compounds in source water at the pilot-scale. At the same time, in the face of extremely low concentrations of perfluorinated compounds in source water (at the ng / L level), the ultrafine powdered activated carbon used in the present invention can achieve a removal rate of 75%-98%. For typical perfluorinated compounds PFOA and PFOS, after being treated by the method proposed in the present invention, the concentrations are both at relatively low levels, meeting the limit standards specified in the "Hygienic Standards for Drinking Water" (GB 5749-2022).

[0142] In addition, the enhanced coagulation technology proposed by the present invention also shows good coagulation and sedimentation effects in actual use. It can reduce the turbidity of the final effluent to 0.03 NTU, effectively remove the ultrafine powdered activated carbon added in the pretreatment section, and avoid additional pollution problems. The above results indicate that the method proposed by the present invention has high practical application value and potential.

[0143] Comparative Example 1

[0144] The difference between this comparative example and Example 2 is only that the activated carbon used is commercially available conventional 200-mesh powdered activated carbon.

[0145] The effect of removing perfluorinated compounds in water in this comparative example is shown in Table 5:

[0146] Table 5

[0147]

[0148] In this comparative example, commercially available conventional 200-mesh powdered activated carbon was used, and its treatment effect on perfluorinated compounds in water was very limited. When facing the pollution situation of 100 ng / L of perfluorinated compounds in water, the removal rate of PFOS by conventional powdered activated carbon was almost 0, and the removal rate of PFOA was only about 20%.

[0149] Comparative Example 2

[0150] The difference between this comparative example and Comparative Example 1 is only that the concentrations of PFOA and PFOS in the raw water are 500 ng / L.

[0151] The effect of removing perfluorinated compounds in water in this comparative example is shown in Table 6:

[0152] Table 6

[0153]

[0154] In this comparative example, when the content of perfluorinated compounds in water is 500 ng / L, the adsorption and removal rate of conventional powdered activated carbon is still low (29% for PFOA and 43% for PFOS), indicating that conventional powdered activated carbon cannot effectively remove perfluorinated compounds.

[0155] Comparative Example 3

[0156] The difference between this comparative example and Example 2 is only that no flocculant is added.

[0157] The results show that: Without adding a flocculant, the performance of the coagulation and sedimentation process will deteriorate, and it is impossible to effectively treat high-turbidity water bodies. Facing ultrafine powdered activated carbon with very small particle sizes, it cannot show good sedimentation and removal effects, resulting in a relatively high turbidity in the final effluent and causing secondary pollution problems. At the same time, under the condition of not adding a flocculant, traditional coagulants also have no removal effect on perfluorinated compounds and will also lead to a decrease in the removal rate of perfluorinated compounds.

[0158] In the description of this specification, the description referring to terms such as "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0159] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for removing perfluorinated compounds in water using ultrafine powdered activated carbon, characterized in that: The method comprises the following steps: Adding activated carbon slurry to the water sample to be treated containing perfluorinated compounds, performing a first stirring treatment, and obtaining a first mixed liquid; adding a coagulant to the first mixed solution, and performing a second stirring process to obtain a second mixed solution; adding a flocculant to the second mixed liquid, and performing a third stirring process to obtain a third mixed liquid; Removing the precipitate in the third mixed solution, thereby achieving the removal of perfluorinated compounds in the water sample to be treated; The activated carbon used in the activated carbon slurry is ultrafine powdered activated carbon, the median particle size of the ultrafine powdered activated carbon is 1 μm-5 μm, and the specific surface area is 900 m 2 / g-1500m 2 / g, the average pore size is 1.5nm-2.0nm, and the total pore volume is 0.4mL / g-0.8mL / g.

2. The method according to claim 1, characterized in that The content of ultrafine powdered activated carbon in the activated carbon slurry is 10wt%-30wt%; Optionally, the content of the ultrafine powdered activated carbon in the first mixed solution is 5 mg / L-40 mg / L.

3. The method according to claim 1, characterized in that The content of the coagulant in the second mixed solution is 5 mg / L-20 mg / L; Optionally, the coagulant includes at least one of polyaluminium chloride, aluminium sulfate, ferric chloride and polyferric sulfate; Optionally, the content of elemental aluminum or elemental iron in the coagulant is ≥ 10 wt%.

4. The method according to claim 1, characterized in that: The content of the flocculant in the third mixed solution is 0.1 mg / L-1 mg / L; Optionally, the flocculant comprises a cationic flocculant; Optionally, the cationic flocculant includes at least one of cationic polyacrylamide and polydimethyldiallylammonium chloride.

5. The method according to claim 1, characterized in that The perfluorinated compound includes at least one of a perfluoroalkyl acid and a perfluoroalkyl sulfonic acid; Optionally, the perfluoroalkyl acid includes at least one of perfluorobutyric acid, perfluoropentanoic acid, perfluorohexanoic acid, perfluoroheptanoic acid, perfluorooctanoic acid, perfluorononanoic acid, and perfluorodecanoic acid; Optionally, the perfluoroalkyl sulfonic acid includes at least one of perfluorobutyl sulfonic acid, perfluorohexyl sulfonic acid, perfluorooctane sulfonic acid, and perfluorodecane sulfonic acid.

6. The method according to claim 1, characterized in that The first stirring treatment time is 5min-30min; Optionally, the stirring intensity of the first stirring treatment is 600 / s-1000 / s in terms of hydraulic gradient; Optionally, the second stirring treatment time is 10s-60s; Optionally, the stirring intensity of the second stirring treatment is 600 / s-1000 / s in terms of hydraulic gradient; Optionally, the third stirring treatment lasts for 10 min to 30 min; Optionally, the stirring intensity of the third stirring treatment is 30 / s-60 / s in terms of hydraulic gradient.

7. The method according to claim 1, characterized in that The method further comprises: Adding a pH regulator to a water sample to be treated containing perfluorinated compounds to adjust the pH value of the water sample to be treated to 6.0-7.5; Optionally, the pH regulator includes an acidic regulator and / or an alkaline regulator; Optionally, the acidic regulator includes at least one of sulfuric acid, hydrochloric acid, nitric acid, and carbon dioxide; Optionally, the alkaline regulator includes at least one of sodium hydroxide, lime and sodium carbonate.

8. The method according to claim 1, characterized in that The step of removing the precipitate in the third mixed solution comprises: The third mixed solution is subjected to a precipitation treatment until the turbidity of the supernatant is less than 1 NTU; The supernatant is filtered until the turbidity of the filtrate is less than 0.3 NTU.

9. The method according to claim 8, characterized in that The precipitation treatment time is 30min-120min.

10. The method according to claim 8, characterized in that The method further comprises: The supernatant is filtered until the turbidity of the filtrate is less than 0.3 NTU, and the pH value of the filtrate is adjusted to 6.5-8.5.

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