Method for removing high-concentration perfluorooctanoic acid

Abstract

The invention discloses a method for removing high-concentration perfluorooctanoic acid, and relates to the technical field of water treatment, in particular to a method for separating and removing high-concentration perfluorooctanoic acid by utilizing micro-nano bubbles, which comprises the following steps: pretreating high-concentration perfluorooctanoic acid wastewater at normal temperature and normal pressure to remove suspended matters; micro-nano bubbles are introduced into the pretreated water body, and perfluorooctanoic acid is promoted to be converted into a hydrophobic polymer by utilizing the synergistic effect of micro-nano bubble hydraulic cavitation and generated strong oxidizing free radicals through adjustment of factors such as gas types, micro-nano bubble treatment time, temperature and flow, so that floating foam is formed on the surface of the water body; and floating foam is separated and removed by a scraper. According to the method, the high-concentration perfluorooctanoic acid in the water body is efficiently removed by adopting the micro-nano bubbles, no extra medicament needs to be added, secondary pollution is avoided, the treatment process is simple to operate, the applicability is wide, and the method has a relatively good application prospect.

Description

Technical Field

[0001] This invention belongs to the field of water treatment technology, specifically relating to a method for removing high concentrations of perfluorooctanoic acid (PFOA). Background Technology

[0002] With accelerated industrialization and changing lifestyles, the number of persistent organic pollutants and emerging pollutants in water bodies is increasing, posing a serious threat to the ecological environment and human health. Traditional water treatment technologies, such as coagulation, sedimentation, and biological treatment, are often ineffective in removing these pollutants, especially emerging pollutants such as perfluoroalkyl substances (PFAS). PFAS are widely detected in the global atmosphere, sediments, organisms, and especially aquatic media, and some monomers can accumulate and amplify through the food chain, exhibiting strong biotoxicity and posing a significant threat to ecosystems and human health. PFOA is one of the most common perfluorinated compounds, capable of accumulating in the human body by binding to proteins and causing health hazards such as kidney and liver damage, immunotoxicity, reproductive toxicity, and cancer.

[0003] To date, methods for treating PFOA in water mainly include adsorption, membrane separation, chemical oxidation, and biological treatment. Patent CN202510120257.9 discloses a hydrophobic porous adsorbent material for removing perfluorooctanoic acid (PFOA) from water, exhibiting excellent adsorption performance and rate at different initial PFOA concentrations. However, its preparation process is complex, and the adsorbent material is difficult to purify, making repeated use difficult. Patent CN202510108304.8 discloses a method for photocatalytic degradation of PFOA in water using boron hydroxides, achieving photocatalytic degradation under different light sources and a relatively wide pH range. However, its reaction time is as long as 40–50 hours, thus limiting the application of this method. Patent CN202010110920.4 discloses a method for removing perfluorinated compounds from environmental water using a polyvinylidene fluoride (PVDF) filter membrane. Based on fluorine-fluorine affinity, it achieves membrane separation of perfluorinated compounds with high adsorption capacity and good selectivity. However, this method requires the use of hazardous organic solvents, the treatment concentration is only at the nanogram level, and the membrane is difficult to reuse. In general, existing methods require a large amount of consumables, are prone to causing secondary pollution, and are complex and time-consuming. Therefore, there is an urgent need to develop an efficient, economical, and environmentally friendly water treatment technology. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of current methods for treating PFOA in water by providing a method for efficiently removing high concentrations of perfluorooctanoic acid (PFOA) from water using micro-nano bubbles.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A method for removing high concentrations of perfluorooctanoic acid (PFOA) includes the following steps: (1) At normal temperature and pressure, wastewater containing high concentration of perfluorooctanoic acid is pretreated to remove suspended solids to obtain pretreated wastewater; (2) Continuously introduce micro-nano bubbles at a temperature of 20-90℃ into the pretreated wastewater to convert perfluorooctanoic acid into a hydrophobic polymer that floats on the surface of the water. The floating matter is removed by scraping with a scraper every 30-60 minutes.

[0006] The method of this invention continuously introduces micro-nano bubbles into pretreated wastewater. During the bubble's ascent, a localized high-temperature, high-pressure environment is formed at the gas-liquid interface. This environment promotes the decomposition of water molecules, generating highly oxidizing hydroxyl radicals (oxidation potential up to 2.8 eV). Hydroxyl radicals (OH) can rapidly oxidize perfluorooctanoic acid (PFOA). Simultaneously, micro- and nano-bubbles, due to their extremely small size and large specific surface area, significantly increase the gas-liquid contact area, improving gas solubility and mass transfer efficiency in water. This provides sufficient oxygen for the oxidation reaction, promoting its progress and increasing the removal efficiency of high-concentration PFOA in wastewater. Furthermore, the presence of micro- and nano-bubbles induces water turbulence, reducing the thickness of the liquid boundary layer and further enhancing mass transfer. This allows PFOA to fully contact and react with oxidants such as hydroxyl radicals, ultimately converting PFOA into a hydrophobic polymer that floats on the water surface. The floating matter can then be scraped off by a scraper, thus achieving PFOA removal. The entire process requires no additional chemical reagents, thus avoiding secondary environmental pollution. It is simple to operate, and the entire process is carried out at normal temperature and pressure. It only requires three core operations: pretreatment, introduction of micro-nano bubbles, and scraping removal, which are easy to control. The required equipment is also relatively simple in structure, easy to maintain, low in cost, and highly environmentally friendly. It has wide applicability to high-concentration perfluorooctanoic acid wastewater under different conditions, with significant removal effect and good application value.

[0007] As a further description of the above technical solution: the concentration of perfluorooctanoic acid in the wastewater containing high concentration of perfluorooctanoic acid in step (1) is 0.100 to 0.400 g / L.

[0008] As a further description of the above technical solution: the pretreatment method for removing suspended solids in step (1) is centrifugal separation, with a centrifuge speed of 3000-8000 r / min and a centrifugation time of 1-3 min, preferably 4000 r / min and 3 min. Centrifugal separation for removing suspended solids is simple to operate and the parameters are controllable, with high treatment efficiency. It can quickly and efficiently remove suspended solids from wastewater, avoid the suspended solids from hindering the subsequent interaction between micro-nano bubbles and perfluorooctanoic acid, clear the interference for the subsequent conversion and removal of perfluorooctanoic acid, and ensure the overall treatment effect. Moreover, centrifugal separation does not require the addition of additional chemical agents, and will not cause secondary pollution due to agent residues. In addition, the equipment is simple to maintain and has no high consumable costs.

[0009] As a further description of the above technical solution: the gas in the micro-nano bubbles in step (2) is nitrogen, oxygen, ozone, or compressed air, with oxygen being preferred. The selected gases are all common and readily available in industry, requiring no special or complex preparation process, and the cost is controllable. Moreover, they are all air components and will not cause secondary pollution. Oxygen is preferred because it can more efficiently help the micro-nano bubbles generate strong oxidizing hydroxyl radicals through hydrodynamic cavitation, improve gas-liquid mass transfer efficiency, and thus promote the conversion of perfluorooctanoic acid into hydrophobic polymers, thereby improving the perfluorooctanoic acid removal rate.

[0010] As a further description of the above technical solution: In step (2), the flow rate of the micro-nano bubbles is 150-250 mL / min, preferably 250 mL / min, to ensure that the micro-nano bubbles are evenly distributed in the wastewater. This avoids the problem of insufficient bubble quantity and low mass transfer efficiency due to excessively low flow rate, which would affect the conversion effect of perfluorooctanoic acid. It also prevents excessively high flow rate from causing gas waste and excessive disturbance to the water body. At this flow rate, the micro-nano bubbles can generate strong oxidizing hydroxyl radicals more fully through the high temperature and high pressure of the gas-liquid interface, while maximizing the gas-liquid contact area and mass transfer efficiency, thus helping perfluorooctanoic acid to be efficiently converted into hydrophobic polymers.

[0011] As a further description of the above technical solution: the duration of introducing micro-nano bubbles in step (2) is 2 to 4 hours. This avoids the situation where the duration is too short, which would prevent perfluorooctanoic acid from being fully converted into hydrophobic polymers by hydrodynamic cavitation and strong oxidizing hydroxyl radicals, while also avoiding the situation where the duration is too long, which would lead to energy waste and slow down the processing efficiency. This is consistent with the core role of micro-nano bubbles in promoting oxidation reactions and enhancing mass transfer.

[0012] Compared with the prior art, the beneficial effects of the present invention are: This invention utilizes the strong oxidizing properties of hydroxyl radicals, the high mass transfer efficiency of micro-nano bubbles, and the ample contact provided by water turbulence to efficiently convert and remove perfluorooctanoic acid (PFOA), achieving a removal rate of over 75%, and approaching 90% in some scenarios. The entire process requires no additional chemical reagents, relying solely on the physicochemical action of micro-nano bubbles for removal, thus avoiding the risk of secondary pollution from reagent residues or hazardous solvents. The entire process is conducted at ambient temperature and pressure, with core steps consisting only of pretreatment, micro-nano bubble introduction, and scraping. Operation is easy to control, and the micro-nano bubble device has a relatively simple structure and is convenient to maintain, requiring no high consumable costs. By adjusting parameters such as bubble type, flow rate, and temperature, it can be adapted to treat high-concentration PFOA wastewater with different initial concentrations. Furthermore, the removal effect is significant, demonstrating good application value. Attached Figure Description

[0013] Figure 1 This is a comparison image of wastewater before and after micro-nano bubble treatment.

[0014] Figure 2 This is a diagram of surface foam after drying. Detailed Implementation

[0015] The claims of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, but this does not constitute any limitation on the present invention. Any limited modifications made by any person within the scope of protection of the claims of the present invention shall still be within the scope of protection of the claims of the present invention.

[0016] Example 1 This embodiment provides a method for removing high concentrations of perfluorooctanoic acid (PFOA) using micro / nano bubble removal technology, including the following steps: At ambient temperature and pressure, 500 mL of wastewater containing 0.400 g / L perfluorooctanoic acid was centrifuged at 4000 r / min for 3 min to separate and remove suspended solids, thus obtaining pretreated wastewater. Micro-nano bubbles with a temperature of 70℃ and oxygen gas were introduced into the pretreated wastewater, with a flow rate of 250 mL / min and a treatment time of 2 h. Surface foam was scraped off every 30 min.

[0017] Wastewater before and after treatment, such as Figure 1 As shown, the wastewater before treatment is a turbid milky white color, with suspended solids and other impurities mixed evenly with the wastewater. After treatment with micro-nano bubbles, the perfluorooctanoic acid in the wastewater is converted into hydrophobic polymers and floats to form obvious foamy scum. The turbidity of the liquid phase changes due to the separation of pollutants, which intuitively demonstrates the effect of micro-nano bubble technology on the conversion and separation of perfluorooctanoic acid.

[0018] After the scraped-off foam dries, it is like Figure 2 As shown, the foam, after drying, appears as a solid / powder, which is a specific manifestation of perfluorooctanoic acid (PFOA) after being converted into a hydrophobic polymer. This proves that after treatment with micro-nano bubbles, PFOA in wastewater is effectively converted into a separable solid phase, achieving the effect of completely removing pollutants from the water.

[0019] After separation, the wastewater was filtered through a 0.22 μm filter membrane, and the concentration of perfluorooctanoic acid (PFOA) was determined by high performance liquid chromatography. The PFOA concentration decreased from 0.400 g / L to 0.0443 g / L, and the PFOA removal rate reached 88.93%.

[0020] Example 2 This embodiment provides a method for removing high concentrations of perfluorooctanoic acid (PFOA) using a micro / nano bubble removal method, comprising the following steps: (1) At room temperature and pressure, 700 mL of wastewater containing 0.300 g / L perfluorooctanoic acid was centrifuged at 4000 r / min for 3 min to separate and remove suspended solids, and pretreated wastewater was obtained. (2) Introduce oxygen micro-nano bubbles at a temperature of 70℃ into the pretreated wastewater, control the flow rate at 250 mL / min, and treat for 2 hours. Every 30 minutes, scrape off the surface foam with a scraper.

[0021] After separation, the wastewater was filtered through a 0.22 μm filter membrane, and its concentration was determined by high performance liquid chromatography. It was found that the concentration of perfluorooctanoic acid (PFOA) decreased from 0.300 g / L to 0.0359 g / L, and the PFOA removal rate reached 88.00%.

[0022] Example 3 This embodiment provides a method for removing high concentrations of perfluorooctanoic acid (PFOA) using a micro / nano bubble removal method, comprising the following steps: (1) At room temperature and pressure, 400 mL of wastewater containing 0.200 g / L perfluorooctanoic acid was centrifuged at 4000 r / min for 3 min to separate and remove suspended solids, and pretreated wastewater was obtained. (2) Introduce oxygen micro-nano bubbles at a temperature of 40℃ into the pretreated wastewater, control the flow rate at 250 mL / min, and treat for 4 hours. Scrape off the surface foam with a scraper every 30 minutes.

[0023] After separation, the wastewater was filtered through a 0.22 μm filter membrane, and its concentration was determined by high performance liquid chromatography. It was found that the concentration of perfluorooctanoic acid (PFOA) decreased from 0.200 g / L to 0.0488 g / L, and the PFOA removal rate reached 75.60%.

[0024] Example 4 This embodiment provides a method for removing high concentrations of perfluorooctanoic acid (PFOA) using a micro / nano bubble removal method, comprising the following steps: (1) At room temperature and pressure, 700 mL of wastewater containing 0.400 g / L perfluorooctanoic acid was centrifuged at 4000 r / min for 3 min to separate and remove suspended solids, and pretreated wastewater was obtained. (2) Compressed air micro-nano bubbles at a temperature of 40℃ are introduced into the pretreated wastewater, the flow rate is controlled at 250 mL / min, the treatment time is 4h, and the surface foam is scraped off by a scraper every 120 min.

[0025] After separation, the wastewater was filtered through a 0.22 μm filter membrane, and its concentration was determined by high performance liquid chromatography. It was found that the concentration of perfluorooctanoic acid (PFOA) decreased from 0.400 g / L to 0.0445 g / L, and the PFOA removal rate reached 88.88%.

[0026] Example 5 This embodiment provides a method for removing high concentrations of perfluorooctanoic acid (PFOA) using a micro / nano bubble removal method, comprising the following steps: (1) At room temperature and pressure, 500 mL of wastewater containing 0.300 g / L perfluorooctanoic acid was centrifuged at 4000 r / min for 3 min to separate and remove suspended solids, and pretreated wastewater was obtained. (2) Introduce oxygen micro-nano bubbles at a temperature of 30°C into the pretreated wastewater, control the flow rate at 150 mL / min, and treat for 2 hours. Every 60 minutes, scrape off the surface foam with a scraper.

[0027] After separation, the wastewater was filtered through a 0.22 μm filter membrane, and its concentration was determined by high performance liquid chromatography. It was found that the concentration of perfluorooctanoic acid (PFOA) decreased from 0.300 g / L to 0.0436 g / L, and the PFOA removal rate reached 85.47%.

[0028] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them; those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions will not cause the essence of the corresponding technical solutions to deviate from the protection scope of the present invention.

Claims

1. A method for removing high concentrations of perfluorooctanoic acid (PFOA), characterized in that, Includes the following steps: At ambient temperature and pressure, wastewater containing high concentrations of perfluorooctanoic acid is pretreated to remove suspended solids, resulting in pretreated wastewater. Micro-nano bubbles at a temperature of 20–90°C are continuously introduced into the pretreated wastewater, causing perfluorooctanoic acid to be converted into a hydrophobic polymer that floats on the surface of the water. The floating matter is then removed by a scraper every 30–60 minutes.

2. The method for removing high-concentration perfluorooctanoic acid according to claim 1, characterized in that: The concentration of perfluorooctanoic acid in the wastewater containing high concentration of perfluorooctanoic acid in step (1) is 0.100 to 0.400 g / L.

3. The method for removing high-concentration perfluorooctanoic acid according to claim 2, characterized in that: The pretreatment method for removing suspended solids in step (1) is centrifugation, with a centrifugation speed of 3000-8000 r / min and a centrifugation time of 1-3 min.

4. The method for removing high-concentration perfluorooctanoic acid according to claim 2, characterized in that: The gas in the micro-nano bubbles in step (2) is nitrogen, oxygen, ozone or compressed air.

5. The method for removing high-concentration perfluorooctanoic acid according to claim 4, characterized in that: The gas in the micro-nano bubbles in step (2) is oxygen.

6. The method for removing high-concentration perfluorooctanoic acid according to claim 4 or 5, characterized in that: In step (2), the flow rate of the micro-nano bubbles introduced is 150-250 mL / min.

7. The method for removing high-concentration perfluorooctanoic acid according to claim 6, characterized in that: The time for introducing micro-nano bubbles in step (2) is 2 to 4 hours.

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