System for treating wastewater containing perfluorinated and polyfluoroalkyl compounds PFAS

Abstract

The utility model relates to the field of wastewater treatment systems, in particular to a system for treating wastewater containing perfluoro and polyfluoroalkyl compounds PFAS. The utility model relates to a system for treating wastewater containing perfluorinated and polyfluoroalkyl compounds PFAS. The system comprises a regulating tank, a flocculation sedimentation tank, an anaerobic-anoxic-aerobic tank, an ultrafiltration membrane system, a nanofiltration membrane system, an oxidation tank, a carbon filter tank and a sludge water treatment system which are arranged in sequence.

Description

Technical Field

[0001] The utility model relates to the field of wastewater treatment systems, and particularly relates to a wastewater treatment system containing perfluoro and polyfluoroalkyl substances (PFAS). Background Art

[0002] Perfluoro and polyfluoroalkyl substances (PFAS) are a new type of persistent organic pollutant. Due to their good chemical stability, thermal stability, and low surface tension, they are widely used in various industrial and consumer products, such as food packaging, textiles, electronic devices, etc. However, the overuse and emission of PFAS have led to their accumulation in the environment, posing a threat to the ecological environment and human health. Therefore, how to effectively remove PFAS from wastewater and reduce its spread in the water environment is an important topic in the current environmental protection field.

[0003] The conventional primary and secondary treatment processes of existing sewage treatment plants have unsatisfactory removal effects on PFAS. To solve this problem, researchers have proposed some new treatment methods, such as adsorption method, advanced oxidation method, membrane separation technology, etc. Among them, the adsorption method mainly uses new nano-adsorbents with high specific surface area, high adsorption capacity, and high affinity to remove PFAS, such as multi-walled carbon nanotubes, graphene-derived materials, metal-organic frameworks, etc. The advanced oxidation method activates oxidants through physical and chemical catalysis to generate strongly oxidizing free radicals to degrade organic pollutants. The membrane separation technology separates pollutants from wastewater physically.

[0004] Although the existing technologies have solved the problem of PFAS removal to a certain extent, there are still some problems and disadvantages. For example, the adsorption method of simply adding common adsorbents such as activated carbon generally has an average removal effect on PFAS, while the preparation cost of new nano-adsorption materials is relatively high. Although the advanced oxidation method has the advantages of high degradation efficiency and no selectivity for pollutants, there are still deficiencies in practical applications, such as dependence on acidic environment, high energy cost, special requirements for reactor design, etc. In addition, these technologies may produce secondary pollution during the treatment process, such as iron sludge, high-salinity wastewater, etc. Summary of the Invention

[0005] The utility model hopes to provide a wastewater treatment system containing perfluoro and polyfluoroalkyl substances (PFAS), and the specific scheme is as follows:

[0006] A wastewater treatment system containing perfluoro and polyfluoroalkyl substances (PFAS) includes a regulating tank, a flocculation sedimentation tank, an anaerobic-anoxic-aerobic tank, an ultrafiltration membrane system, a nanofiltration membrane system, an oxidation tank, a carbon filtration tank, and a sludge and wastewater treatment system arranged in sequence.

[0007] The flocculation sedimentation tank is connected to the sludge and wastewater treatment system through pipelines, and the anaerobic-anoxic-aerobic tank is connected to the sludge and wastewater treatment system through pipelines.

[0008] A flocculant pipeline is provided on the flocculation sedimentation tank.

[0009] An ozone pipeline is provided in the oxidation tank.

[0010] The ultrafiltration membrane system and the regulation tank are connected through pipelines.

[0011] The present utility model mainly adopts the following technical means:

[0012] 1. Adopt the membrane pretreatment technology (ultrafiltration membrane system): First, the wastewater to be treated is pretreated through the ultrafiltration membrane to remove large particulate matters and suspended solids, so as to reduce the burden on the subsequent treatment units and improve the treatment efficiency. The ultrafiltration membrane in this technical solution can be a hollow fiber ultrafiltration membrane or a spiral wound ultrafiltration membrane.

[0013] 2. Adopt the nanofiltration technology (nanofiltration membrane system): The wastewater treated by the ultrafiltration membrane is further treated through the nanofiltration membrane to remove PFAS in the water. The nanofiltration membrane has a relatively high molecular weight cut-off, which can effectively remove PFAS in the water. At the same time, the operating pressure of the nanofiltration membrane is relatively low, and the energy consumption is relatively small, which is beneficial to energy conservation. After the wastewater is treated by the nanofiltration membrane, PFAS is concentrated in the concentrated water, and the produced water is relatively clean water.

[0014] 3. Adopt the advanced oxidation technology (oxidation tank): The nanofiltration concentrated water is deeply treated through the advanced catalytic oxidation technology to further decompose PFAS in the wastewater. The advanced oxidation technology can generate strongly oxidizing free radicals, which can effectively degrade PFAS in the water, and the reaction conditions are mild and no secondary pollution will be generated. In this technical solution, the advanced oxidation process with the combination of "ultraviolet + ozone" is selected. The ultraviolet light and ozone act synergistically to generate strongly oxidizing hydroxyl free radicals to decompose PFAS in the nanofiltration concentrated water. This process does not require pH adjustment of the wastewater and will not generate secondary pollution. The unreacted ozone will decompose into oxygen and escape into the air.

[0015] 4. Adopt the biological activated carbon filtration technology (carbon filter tank): Finally, the wastewater after advanced oxidation is filtered by the biological activated carbon filter tank. The biological activated carbon filter tank uses granular activated carbon as the filter material. By adjusting the operation mode and inoculating bacteria agents, etc., a biological film with biological degradation function can grow on the surface of the activated carbon. Through the dual effects of activated carbon adsorption and biological degradation, PFAS in the wastewater is further treated to ensure that the final effluent quality meets the standards.

[0016] 5. Integrated Optimization: Integrate the above four technologies in a processing system to form an efficient membrane-based integrated process for water purification based on "ultrafiltration pretreatment + nanofiltration + advanced oxidation + biological activated carbon filtration". This integrated optimization method takes membrane separation technology as the core and other physical and chemical treatment methods as supplements, giving full play to the advantages of various technologies, overcoming the deficiencies of single technologies, and achieving efficient removal of PFAS in wastewater.

[0017] The beneficial effects of the present utility model are as follows:

[0018] 1. Adopting a new integrated system of high-efficiency membrane-based coupling for water purification of "ultrafiltration pretreatment + nanofiltration + advanced oxidation + biological activated carbon filtration" can effectively remove PFAS in wastewater, breaking through the bottleneck of the weak ability of traditional treatment processes to remove new pollutants, and achieving efficient removal of PFAS in wastewater.

[0019] 2. The present utility model uses membrane-based technology as the core technology. Compared with traditional adsorption methods and advanced oxidation methods, membrane-based technology has higher treatment efficiency and a wider scope of application, can effectively meet the treatment requirements of different types of new pollutants, and has less difference in the removal effect of PFAS.

[0020] 3. The membrane-based technology adopted by the present utility model has lower preparation costs and operating costs compared with traditional adsorption methods and advanced oxidation methods, which is conducive to popularization and application. At the same time, the membrane-based technology does not produce secondary pollution, such as iron sludge, high-salinity wastewater, etc., during the treatment process, and is more environmentally friendly.

[0021] The membrane-based technology of the present utility model can be effectively combined with other water treatment technologies, such as biological treatment, chemical precipitation, etc., to form a more comprehensive and efficient water treatment system, further improving the water treatment effect. Description of the Drawings

[0022] Figure 1 It is a schematic structural diagram of a wastewater treatment system containing per- and polyfluoroalkyl substances (PFAS) of the present utility model;

[0023] Wherein the reference numerals: 1. Regulation tank; 2. Flocculation sedimentation tank; 3. Anaerobic-anoxic-aerobic tank; 4. Ultrafiltration membrane system; 5. Nanofiltration membrane system; 6. Oxidation tank; 7. Carbon filtration tank; 8. Sludge and wastewater treatment system. Detailed Embodiments

[0024] The following is further described in conjunction with Figure 1 for further illustration:

[0025] A wastewater treatment system containing per- and polyfluoroalkyl substances (PFAS) includes a regulation tank 1, a flocculation sedimentation tank 2, an anaerobic-anoxic-aerobic tank 3, an ultrafiltration membrane system 4, a nanofiltration membrane system 5, an oxidation tank 6, a carbon filtration tank 7, and a sludge and wastewater treatment system 8 arranged in sequence.

[0026] The flocculation sedimentation tank 2 is connected to the sludge treatment system 8 through a pipeline, and the anaerobic-anoxic-aerobic tank 3 is connected to the sludge treatment system 8 through a pipeline.

[0027] A flocculant pipeline is provided on the flocculation sedimentation tank 2.

[0028] An ozone pipeline is provided in the oxidation tank 6.

[0029] The ultrafiltration membrane system 4 and the regulation tank 1 are connected through a pipeline.

[0030] The operation steps of a wastewater treatment system for per- and polyfluoroalkyl substances (PFAS) of the present utility model are as follows:

[0031] Step 1: The wastewater containing PFAS enters the regulation tank 1 to regulate the water volume and quality, avoiding affecting the subsequent treatment process due to fluctuations in water quality and volume.

[0032] Step 2: The water discharged from the regulation tank 1 enters the flocculation sedimentation tank 2. Flocculation is the process of aggregating colloidal particles and tiny suspended solids in water by adding coagulants. The flocculation methods that can be adopted in the flocculation zone include mechanical agitation, grid flocculation, and folded-plate flocculation, etc. The coagulants used can be one or several of flocculants such as polyaluminum chloride (PAC) and polyacrylamide (PAM). The flocculation time is generally 10 - 30 minutes. Sedimentation refers to the process of separating the aggregates (also called flocs) formed by flocculation from the wastewater. The sedimentation zone can adopt inclined plate sedimentation tanks, inclined tube sedimentation tanks, etc. The wastewater removes suspended solids, colloids and other substances in the water through the flocculation sedimentation tank and then enters the biochemical tank.

[0033] Step 3: The biochemical tank adopted in this technical solution is based on the traditional "anaerobic + anoxic + aerobic (i.e., anaerobic-anoxic-aerobic tank 3)" process (AAO) modified "anaerobic + anoxic + moving bed biofilm" process (AAMBBR), that is, suspended packing is added to the aerobic tank. The suspended packing provides a growth carrier for the activated sludge, and the activated sludge adheres to the packing to form a biofilm. Aerobic bacteria, anoxic bacteria, anaerobic bacteria, etc. are distributed from the outside to the inside of the biofilm. The addition of the suspended packing reduces the loss of activated sludge, increases the sludge concentration, and improves the shock resistance of the aerobic tank. It should be noted that the removal of PFAS in the biochemical tank mainly relies on the adsorption of sludge, and decomposition only accounts for a small part. Secondly, PFAS has certain biological toxicity, and the sludge needs to have a certain shock resistance. Therefore, adopting the process combination form of AAMBBR can improve the sludge concentration and shock resistance of the biochemical tank to cope with PFAS in the wastewater. In addition, in order to strengthen the decomposition of PFAS by the activated sludge, special bacterial agents can be added to the biochemical tank for inoculation to improve the decomposition ability of the activated sludge for PFAS. Adopting the combination form of AAMBBR does not require the setting of a secondary sedimentation tank, reducing the floor area of the equipment.

[0034] Step 4: The effluent from the biochemical pool (i.e., the anaerobic-anoxic-aerobic tank 3) enters the ultrafiltration membrane system 4. The system is set with an operating pressure of 0.1 MPa, an operating temperature of 25 °C, and the average pore size of the ultrafiltration membrane is 0.03 μm to remove large particulate matter and suspended solids. During this process, the flux of the ultrafiltration membrane remains above 100 L / (m 2 ·h) to ensure the treatment efficiency.

[0035] Step 5: Nanofiltration treatment. The wastewater treated by the ultrafiltration membrane is introduced into the nanofiltration membrane system 5. The operating pressure is set at 1.5 MPa, the operating temperature is 30 °C, and the molecular weight cut-off of the nanofiltration membrane is 200 Da. The nanofiltration membrane system 5 is a key link for removing PFAS from water. During this process, the flux of the nanofiltration membrane remains above 50 L / (m 2 ·h) to ensure the treatment efficiency. The water produced by the nanofiltration membrane meets the standards and is discharged, and PFAS is concentrated in the concentrated water and enters the oxidation tank for further treatment.

[0036] Step 6: The oxidation tank 6 adopts the advanced oxidation process of "ultraviolet + ozone" to oxidize and decompose PFAS. The oxidation tank 6 is in the form of an ozone contact oxidation tank, and several ultraviolet lamp tubes are arranged in parallel along the length direction at the top of the oxidation tank. The ultraviolet intensity in the tank is above 140 mJ / cm 2 above.

[0037] Step 7: The effluent from the oxidation tank 6 enters the carbon filter tank 7, and PFAS is further removed through the adsorption and biodegradation of biological activated carbon. The water produced by the biological activated carbon filter meets the standards and is discharged. The above are the specific operation steps of this embodiment. Through this method, PFAS in the wastewater can be effectively removed.

[0038] The utility model can effectively remove perfluoro and polyfluoroalkyl substances in water. Secondly, this technical solution combines technologies such as membrane pretreatment and advanced oxidation. Compared with traditional treatment methods, it has higher treatment efficiency and lower operating costs, which is very attractive to sewage treatment plants, chemical enterprises, etc. Finally, this technical solution can also reduce the generation of secondary pollution, such as iron sludge, high-salinity wastewater, etc.

[0039] Although the embodiments of the utility model have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principle and spirit of the utility model. The scope of the utility model is defined by the appended claims and their equivalents.

Claims

1. A wastewater treatment system containing per- and polyfluoroalkyl substances (PFAS), characterized in that: It includes a regulating pond, a flocculation sedimentation tank, an anaerobic-anoxic-aerobic tank, an ultrafiltration membrane system, a nanofiltration membrane system, an oxidation pond, a carbon filter tank, and a sludge and wastewater treatment system arranged in sequence; the flocculation sedimentation tank is connected to the sludge and wastewater treatment system through a pipeline, and the anaerobic-anoxic-aerobic tank is connected to the sludge and wastewater treatment system through a pipeline; the ultrafiltration membrane system and the regulating pond are connected through a pipeline.

2. The wastewater treatment system containing per- and polyfluoroalkyl substances (PFAS) as described in claim 1, wherein: A flocculant pipeline is provided on the flocculation sedimentation tank.

3. The wastewater treatment system containing perfluoro and polyfluoroalkyl substances (PFAS) as described in claim 1, wherein: An ozone pipeline is provided in the oxidation pond.

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