Adsorption-coagulant for removing perfluorinated compounds in water and application of adsorption-coagulant

Abstract

The invention is applicable to the technical field of perfluorinated compound removal, and provides an adsorption-coagulant for removing perfluorinated compounds in water and application thereof, the adsorption-coagulant comprises an adsorbent and a coagulant, the adsorbent adopts activated carbon powder, and the coagulant adopts polyaluminum chloride. The adsorbent adopted by the invention can efficiently capture trace perfluoroalkyl molecules in water, and the coagulant can promote the molecules to form larger aggregates in water, so that the overall removal efficiency is improved. By reasonably designing the adsorption-coagulation process, the use amount of a traditional coagulant can be reduced, the generation of byproducts in the treatment process is reduced, and the subsequent treatment cost is reduced, so that the economical efficiency and sustainability of the whole treatment process are improved. The adsorption-coagulation technology disclosed by the invention combines two water treatment methods of adsorption and coagulation, the removal efficiency of nondegradable pollutants such as perfluorinated compounds is remarkably improved through the combined action of the two methods, and the adsorption-coagulation technology shows wide applicability.

Description

Technical Field

[0001] The invention belongs to the technical field of perfluorinated compound removal, and in particular relates to an adsorption-coagulant for removing perfluorinated compounds in water and application thereof. Background Art

[0002] Due to the extensive use of products containing perfluorinated compounds (PFASs) and the discharge of industrial wastewater, sewage treatment plants have become an important gathering place for perfluorinated compound pollutants, and thus an important source of perfluorinated compound pollution in natural water bodies and drinking water bodies. Traditional sewage treatment mostly uses sedimentation, filtration (first-order treatment technology) and biological treatment (second-order treatment technology). The first-order treatment technology has almost no effect on the concentration of perfluorinated compounds. The second-order treatment technology often leads to an increase in the concentration of perfluorooctane sulfonic acid compounds and perfluorooctanoic acid in the effluent due to the biodegradation of its precursors.

[0003] For high-concentration fluoride-containing industrial wastewater, the calcium salt precipitation method is generally used, that is, adding lime to the wastewater to remove fluoride ions and calcium ions by forming CaF2 precipitates. This process has the advantages of simple method, convenient treatment, and low cost, but it has disadvantages such as it is difficult for the treated effluent to meet the standards, the sludge sedimentation is slow, and dehydration is difficult. In addition, the aluminum salt coagulation precipitation method is also used, but it has disadvantages such as a small scope of use, a large amount of coagulant required if the fluoride content is high, high treatment costs, and a large amount of sludge generated. At the same time, the adsorption method is suitable for deep treatment of drinking water with a small amount of water. Most adsorbents play an anion exchange role, so the fluoride removal effect is very obvious, but special treatment agents need to be added and specific equipment needs to be set up. The treatment cost is often higher than the precipitation method, and the operation is complicated. The fluoride ion removal effect is also affected by operating factors such as stirring conditions and sedimentation time, as well as SO4 in the water. 2- 、C1 - The influence of anions is relatively large, and the effluent quality is not stable enough. This is related to the current insufficient understanding of the coagulation defluoridation mechanism. Therefore, studying the coagulation defluoridation mechanism has obvious practical significance.

[0004] Due to their strong water solubility, perfluorinated compounds cannot be effectively degraded during the sewage treatment process and are easily transferred to the sludge. The land use process of the sludge will lead to the risk of perfluorinated compounds spreading to the soil. The traditional activated sludge sewage treatment process has a low degradation effect on perfluorinated compounds in the sludge, which affects the resource utilization of the sludge. The biological method commonly used in existing sewage treatment plants cannot achieve the purpose of removing perfluorinated compounds, resulting in the continuous accumulation of perfluorinated compounds in nature and the gradual expansion of the pollution area. Simple photocatalytic treatment requires large-scale adjustments to the existing sewage treatment process, adding processes and equipment modifications, consuming a lot of manpower and material resources, and has high energy consumption, low efficiency, and large limitations on the pollutants treated. Some researchers have tried to use photocatalysis and microbial treatment in different devices in stages. The sewage is first pretreated by photocatalysis before entering the biodegradation device. The operation process is complicated, the degree of pretreatment is difficult to control, and the subsequent process is greatly affected by the degree of pretreatment, which increases the difficulty of regulation.

[0005] In view of the above problems, the present invention proposes an adsorption-coagulant for removing perfluorinated compounds in water and its application. Summary of the invention

[0006] The object of the present invention is to provide an adsorption-coagulant for removing perfluorinated compounds in water and its application, aiming to solve the problems raised in the above background technology.

[0007] The purpose of the present invention is achieved through the following technical solutions:

[0008] An adsorption-coagulant for removing perfluorinated compounds in water comprises an adsorbent and a coagulant. The adsorbent is activated carbon powder and the coagulant is polyaluminium chloride.

[0009] Furthermore, the particle size of the activated carbon powder is less than 0.1 mm, the zero charge point is 7.5, and the specific surface area is 812 m 2 ·g -1 .

[0010] Furthermore, the polyaluminium chloride contains 29% of aluminium oxide.

[0011] An application of the adsorption-coagulant described above in removing perfluorinated compounds from water.

[0012] Furthermore, the perfluoro compound is a perfluoroalkanoic acid compound, and the perfluoroalkanoic acid compound includes perfluorooctanoic acid and perfluorooctane sulfonic acid.

[0013] Compared with the prior art, the present invention has the following beneficial effects:

[0014] 1. Enhanced removal efficiency: The adsorbent used in the present invention can efficiently capture trace amounts of perfluoroalkyl molecules in water, while the coagulant can promote these molecules to form larger aggregates in water, thereby improving the overall removal efficiency.

[0015] 2. Reduce treatment costs: The present invention can reduce the use of traditional coagulants by rationally designing the adsorption-coagulation process, which not only reduces the generation of by-products during the treatment process, but also reduces subsequent treatment costs, thereby improving the economy and sustainability of the entire treatment process.

[0016] 3. Wide applicability: The adsorption-coagulation technology of the present invention combines the two water treatment methods of adsorption and coagulation. The combined action of these two methods significantly improves the removal efficiency of difficult-to-degrade pollutants such as perfluorinated compounds, showing wide applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The PACl dosage for PFAAs affects the results.

[0018] Figure 2 The pH value affects the results for PFAAs.

[0019] Figure 3 Temperature effect results for PFAAs.

[0020] Figure 4 The different initial turbidities of PFAAs affect the results.

[0021] Figure 5 Different initial concentrations of PFAAs affect the results.

[0022] Figure 6 The results show the effect of activated carbon powder dosage on the removal of residual turbidity in PFOA solutions with different initial concentrations.

[0023] Figure 7 This is the effect of the dosage of activated carbon powder on the residual PFOA content in water.

[0024] Figure 8 The results show the effect of activated carbon powder dosage on the removal of residual turbidity in PFOS solutions with different initial concentrations.

[0025] Fig. 9 The results show the effect of activated carbon powder dosage on the residual PFOS content in water.

[0026] Fig.10 Schematic diagram of the coagulation process. DETAILED DESCRIPTION

[0027] In order to have a clearer understanding of the technical features, purposes and beneficial effects of the present invention, the technical solution of the present invention is now described in detail below, but it should not be understood as limiting the scope of the present invention. The experimental methods described in the following examples are conventional methods unless otherwise specified; the reagents and materials can be obtained from commercial sources unless otherwise specified.

[0028] The effluent treated by the sewage treatment plant in this experiment mainly comes from the sewage treatment plant in the northern suburbs of Changchun. The standard samples and internal standard samples of perfluoroalkanoic acid compounds (PFAAs) used in this experiment were purchased from Wellington Company in Canada. Among them, PFAAs include perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS). PFAAs are a type of perfluorinated compound (PFAS). Ammonium acetate and methanol (HPLC grade) were purchased from JTBaker Company in the United States. Polyaluminium chloride (PACl, Al2O3=29%) was purchased from Changchun Water Purifier Agency. Activated carbon powder (PAC, particle size less than 0.1mm) has a charge zero point of 7.5 and a specific surface area of ​​812m 2 ·g -1 .

[0029] Example 1. Effects of the dosage of coagulant (PACl) and water quality (pH, temperature, initial turbidity of water sample, initial concentration of PFAAs, etc.) on the removal of PFAAs;

[0030] The turbidity of the raw water is about 2NTU. Since the turbidity of the raw water is low and does not meet the requirements of the coagulation experiment, this experiment placed the raw water in a container to allow the particles to settle naturally. The turbidity of the treated water sample is about 6.5NTU and is used for the coagulation experiment. The pH value of the experimental water is 7.6, and the organic carbon content is 62.5mg·L -1 (Setting when water sample turbidity and pH value are not variables).

[0031] ① Impact of PACl dosage: Fig.10 As shown in Figure 2, 0.2 mg / L PFAAs was added to 1 L of water and mechanically stirred for 12 h. After equilibrium, PACl was used to remove suspended solids (SS) in the water at room temperature. The effect of PACl dosage on the removal of PFAAs and turbidity in water is shown in Figure 2. Figure 1 As shown, Figure 1 The content distribution of PFAAs in the supernatant (Water), suspended solids (SS) and precipitate (Precipitate) after the coagulation experiment and the residual turbidity of the solution (Residual turbidity) are shown in the figure. As can be seen from the figure, with the increase of PACl dosage (0-10mg·L -1 ), the residual turbidity of the solution continued to decrease, and then PACl was added to increase its concentration from 10 mg·L-1 Increase to 15mg·L -1 , the residual turbidity of the solution did not change much. At the same time, the SS curve showed a downward trend, indicating that coagulation can remove SS in water. With the increase of PACl dosage, the content of PFAAs (including PFOA and PFOS) showed a downward trend, which shows that coagulation can not only remove SS in water, but also reduce the content of PFAAs in water.

[0032] ② pH value affects the solution: The effect of pH value on the removal of PFAAs and solution turbidity during coagulation is shown in Figure 2 . As the pH value of the solution increases, the residual turbidity of the solution decreases significantly. This is mainly because the zero-point potential of suspended solids (SS) is around 5.8. When the pH value of the solution is higher than 5.8, the surface charge of SS becomes negative, and the electrostatic attraction between the positively charged PACl and the negatively charged SS increases, which promotes the removal of SS. Therefore, the increase in the pH value of the solution is conducive to the removal of SS in the solution. In contrast to the change process of the residual turbidity of the solution, the concentration of PFAAs in the supernatant increases with the increase in pH. The removal of PFAAs in water is related to the properties of SS and the morphology of PACl under different pH conditions. When the pH is less than 5.8, since PFAAs exist in the form of anions under experimental conditions, they can be easily adsorbed on the surface of positively charged SS through electrostatic attraction. At the same time, the concentration of aluminum ions dissociated from PACl is also relatively high, which helps PACl adsorb more PFAAs during the coagulation process. Therefore, under low pH conditions, both PACl and SS are conducive to the removal of PFAAs.

[0033] ③The influence of temperature: Temperature is an important factor affecting the coagulation effect. Too low temperature will affect the hydrolysis of PACl, increase the viscosity of water, and reduce the coagulation efficiency. Figure 3 The effect of temperature on the removal of PFAAs and turbidity during coagulation was shown. As the temperature of the solution increased, the content of PFAAs in the supernatant gradually increased, while the residual turbidity of the solution decreased with the increase in temperature. Since the coagulation efficiency is significantly affected by temperature, lower temperatures reduce the collision efficiency and the coagulation efficiency, resulting in a higher residual turbidity of the solution under low temperature conditions. The content of PFAAs in the supernatant is lower under low temperature conditions, indicating that more PFAAs are adsorbed on the surface of suspended solids (SS) during coagulation. This also proves that the adsorption process of PFAAs on SS is an exothermic process, that is, the ability of SS to adsorb PFAAs under low temperature conditions is higher than that under high temperature conditions. In addition, PFAAs are a type of surfactant. The greater the amount of PFAAs adsorbed on SS under low temperature conditions, the better the stability of SS in water, which contributes to the increase in the residual turbidity in water.

[0034] ④ Effect of initial turbidity: Suspended solids (SS) were added to the raw water to obtain water samples with different turbidities (0-10.5 NTU). The effect of initial turbidity on the removal of PFAAs and residual turbidity is shown in Figure 4 When the initial turbidity is low, the residual concentration of PFAAs in the supernatant is high. During the coagulation process, particles in water with low turbidity are not easy to form aggregates, resulting in low coagulation efficiency. On the contrary, water with high turbidity contains more SS, which can adsorb more PFAAs from the water, resulting in a significant decrease in the residual concentration of PFAAs in the water. When the initial turbidity reaches 10.5 NTU, 10 mg·L -1 When PACl was used as coagulant, the residual concentrations of PFOA and PFOS in the supernatant were reduced to 0.563 μg·L -1 and 0.896 μg·L -1 .

[0035] ⑤ Effect of initial concentration of PFAAs: 0.1 mg·L -1 , 0.2mg·L -1 , 0.5mg·L -1 , 1.0mg·L -1 , 2.0mg·L -1 、3.0mg·L -1 The PFAAs were mechanically stirred for 12 h before coagulation test. The dosage of PACl was 10 mg·L -1 , the coagulation temperature is room temperature. As can be seen from the figure, the concentration of PFAAs in the supernatant increases with the increase of the initial concentration of PFAAs, and the content of PFAAs in suspended matter and sediment also increases with the increase of the initial concentration of PFAAs. As the initial concentration of PFAAs in water continues to increase, the residual turbidity in the water continues to decrease. Under high concentration PFAAs conditions, PFAAs adsorb on SS to make it more stable. This may be because when the PFAAs content is high, SS adsorbs more PFAAs, making it more negatively charged, which makes it easier for positively charged PACl to adsorb SS, thereby effectively removing SS during the coagulation process.

[0036] Example 2: Combined removal of PFAAs from water by adsorption-coagulation;

[0037] The turbidity of the raw water is about 2NTU. Since the turbidity of the raw water is low and does not meet the requirements of the coagulation experiment, this experiment placed the raw water in a container to allow the particles to settle naturally. The turbidity of the treated water sample is about 6.5NTU and is used for the coagulation experiment. The pH value of the experimental water is 7.6, and the organic carbon content is 62.5mg·L -1 .

[0038] A simulation experiment was conducted using PFOA and PFOS. 0.5 mg·L -1 , 1mg·L -1 , 3mg·L -1 PFOA and PFOS were adsorbed in the solid-liquid phase and mechanically stirred for 12 hours to achieve equilibrium in the distribution of PFOA. 1 mg, 5 mg, 10 mg, 15 mg, and 20 mg of activated carbon powder were added to three water samples with different PFOA concentrations, and mechanically stirred for 12 hours to achieve equilibrium in the adsorption of PFOA and PFOS by activated carbon. Coagulation experiments were carried out at room temperature. The dosage of PACl was 10 mg·L -1 .

[0039] We studied the removal efficiency of PFOA under the combined action of adsorption and coagulation. Figure 6 As shown, after adding 1 mg·L -1 After adding activated carbon powder, the residual turbidity in the water dropped significantly. The residual turbidity in the water changed little after continued addition of activated carbon. This shows that in the adsorption-coagulation process, the initial concentration of PFOA has little effect on the removal of residual turbidity in the water. Figure 7 The effect of the amount of activated carbon powder added during the adsorption-coagulation process on the residual PFOA content in the water is shown. As can be seen from the figure, the greater the amount of activated carbon powder added, the lower the residual PFOA content in the water. When the initial concentration of PFOA is 0.5 mg·L -1 When the dosage of activated carbon powder is 1 mg·L -1 , the residual PFOA content in water is less than 1μg·L -1 ; When the initial concentration of PFOA is 1 mg·L -1 When the dosage of activated carbon powder is 10 mg·L -1 , the residual PFOA content in water is less than 1μg·L -1 ; When the initial concentration of PFOA was 3 mg·L -1 When the dosage of activated carbon powder is 15 mg·L -1 , the residual PFOA content in water is less than 1μg·L -1 Therefore, when a pollution accident occurs, PFOA in the water can be effectively removed by first adding activated carbon powder and then coagulating.

[0040] We studied the removal efficiency of PFOS under the combined action of adsorption and coagulation. Figure 8 As shown, after adding 1 mg·L -1 After adding activated carbon powder, the residual turbidity in the water dropped significantly. With the continued addition of activated carbon, the residual turbidity in the water first decreased and then increased. This shows that in the adsorption-coagulation process, the initial concentration of PFOS has little effect on the removal of residual turbidity in the water. Fig. 9The effect of PAC dosage on the residual PFOS content in the water during the adsorption-coagulation process is shown. As can be seen from the figure, the greater the PAC dosage, the lower the residual PFOS content in the water. When the initial concentration of PFOS is 0.5 mg·L -1 When the dosage of PAC is 1 mg·L -1 , the residual PFOS content in water is less than 1μg·L -1 ; When the initial concentration of PFOS was 1 mg·L -1 When the dosage of PAC is 10 mg·L -1 , the residual PFOS content in water is less than 1μg·L -1 ; When the initial concentration of PFOS was 3 mg·L -1 When the dosage of PAC is 20 mg·L -1 , the residual PFOS content in water is less than 2μg·L -1 Therefore, when a pollution accident occurs, PFOS in the water can be effectively removed by first adding activated carbon powder and then coagulating.

[0041] The above are only preferred embodiments of the present invention. It should be pointed out that, for those skilled in the art, several modifications and improvements can be made without departing from the concept of the present invention. These should also be regarded as the protection scope of the present invention. These will not affect the effect of the implementation of the present invention and the practicality of the patent.

Claims

1. An adsorption-coagulant for removing perfluorinated compounds from water, It is characterized in that The adsorption-coagulant comprises an adsorbent and a coagulant, wherein the adsorbent is activated carbon powder and the coagulant is polyaluminium chloride.

2. The adsorption-coagulant according to claim 1, It is characterized in that The particle size of the activated carbon powder is less than 0.1 mm, the zero charge point is 7.5, and the specific surface area is 812 m 2 ·g -1 .

3. The adsorption-coagulant according to claim 1, It is characterized in that The polyaluminium chloride contains 29% of aluminium oxide.

4. Use of the adsorption-coagulant according to any one of claims 1 to 3 in removing perfluorinated compounds from water.

5. The use according to claim 4, It is characterized in that The perfluoro compound is a perfluoroalkanoic acid compound, and the perfluoroalkanoic acid compound includes perfluorooctanoic acid and perfluorooctane sulfonic acid.

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