Sustainable purification method based on nanobubbles

Abstract

The invention discloses a sustainable purification method based on nanobubbles, and relates to the technical field of water treatment. The sustainable purification method based on the nanobubbles comprises the following steps: preparing a nanobubble solution through a nanobubble generator; mixing the nano-bubble solution with hydrogen persulfate to activate the hydrogen persulfate, and promoting decomposition of the hydrogen persulfate on a nano-bubble interface to generate free sulfate radicals; the peroxydisulfate is used for water treatment and purification after being activated. By means of the innovative structural design and the utilization of the characteristics of the nano bubbles, the oxidative degradation efficiency is improved, meanwhile, the purification capacity can be kept as long as several months, low-energy-consumption, pollution-free and sustainable green environment restoration is achieved, and an efficient, environment-friendly and economical new way is provided for water pollution treatment.

Description

Technical Field

[0001] The present invention belongs to the technical field of water treatment, and particularly relates to a sustainable purification method based on nanobubbles. Background Art

[0002] With the development of industry, the increasing number of micropollutants in water bodies has raised concerns about the ecosystem and drinking water safety. These pollutants are complex, hidden, and persistent. Traditional water treatment processes, such as coagulation, sedimentation, filtration, disinfection, etc., have limited removal effects on them and cannot achieve complete mineralization. Therefore, it is imperative to develop efficient, convenient, and environmentally friendly water treatment technologies for purification.

[0003] Currently, the following methods are available for the removal of micropollutants: 1) Fenton method / Fenton-like method: The traditional Fenton reaction uses Fe 2+ to catalyze the decomposition of hydrogen peroxide to generate hydroxyl radicals (·OH), and requires an acidic environment (pH 2-4) to avoid the precipitation of Fe 3+ . The Fenton-like reaction is an extension and improvement of the traditional Fenton reaction. Its core lies in activating the oxidant by replacing the catalyst or introducing external energy input to generate strongly oxidizing radicals (such as ·OH, SO4 - ·, etc.) for degrading refractory organic compounds. Compared with the traditional Fenton reaction, the Fenton-like reaction is more flexible in terms of catalyst selection, reaction condition adaptability, and oxidation efficiency.

[0004] 2) Electrochemical method: Flocculants (such as Al 3+ / Fe 3+ ) are generated through electrode reactions or pollutants are directly oxidized.

[0005] 3) Persulfate method: Persulfate needs to be activated to generate sulfate radicals (SO4 - ·) and active species such as ·OH, and can be activated by heating, transition metals, carbon-based materials, and alkalinity.

[0006] The above methods for removing micropollutants all have limitations: 1) Reagent consumption and cost issues: The Fenton method requires continuous addition of hydrogen peroxide and Fe 2+ , and several kilograms of reagents may be consumed in treating wastewater. The efficient electrodes of the electrochemical method require precious metals (such as Pt) or boron-doped diamond (BDD). The material cost accounts for more than 60% of the total system cost. The reaction needs to maintain a high current density to generate sufficient oxidizing substances. Therefore, there are problems such as high electrode material cost, high energy consumption, and difficulty in large-scale application. Thermal activation of persulfate requires continuous heating, and transition metal activation (such as Co 2+ ) is toxic and requires additional immobilization treatment. The removal and mineralization of pollutants will terminate when the external energy input stops and the activator is exhausted.

[0007] 2) Harsh reaction conditions: The Fenton reaction requires strict regulation of pH to acidic, and a large amount of iron-containing sludge is produced after neutralization. The alkaline activation of persulfate requires maintaining pH > 10, which is difficult to stably control in actual water bodies.

[0008] 3) By-product risks: Incomplete mineralization may produce more toxic intermediate products (such as chlorinated organic compounds, quinones).

[0009] Potassium peroxymonosulfate (PMS) is an oxidant widely used in the field of water treatment. Due to its strong oxidation ability and environmentally friendly characteristics, it is used to remove refractory organic pollutants in water (such as pesticides, pharmaceutical residues, dyes, and persistent organic pollutants). Its oxidation ability is limited by itself, and a large number of free radicals need to be released through activation to achieve stronger oxidation ability. There is a peroxy bond (O-O) in the persulfate molecule, and this bond is the core of its active oxidation characteristics. After the cleavage of the O-O bond, a large number of sulfate radicals (SO4 - ·) are released, and secondary free radicals (such as •OH) are further generated, thereby attacking and degrading organic pollutant molecules in water.

[0010] In the existing technologies, the methods for activating persulfate (PMS) generally have the problem of high energy consumption. When the external energy input stops and the activator is exhausted, the removal and mineralization of pollutants will be terminated. Continuous high energy and chemical input will lead to high operating costs and potential secondary pollution. Moreover, the preparation processes of traditional catalytic materials (such as CuCo2O4, LnMnO3, etc.) are complex, and the material costs are high, which are difficult to meet the requirements of large-scale water treatment applications. In addition, the existing catalytic methods may bring secondary pollution risks due to the release of heavy metal ions and other by-products during the catalyst or activation process.

[0011] The diameter of nanobubbles is less than 1 micron, and they have a huge specific surface area and can stably exist for several months. Their stability helps to continuously activate persulfate during long-term storage, achieving sustainable and economically feasible pollutant removal.

[0012] Currently, there have been studies on activating persulfate (PMS) with nanobubbles, but most of them still require the addition of other agents, such as chloride ions Cl-. The addition will significantly affect the taste of water, resulting in bitter and salty water. Secondly, the reactive chlorine substances generated will lead to the formation of by-products and affect health. There are also studies on the combined use of microbubbles and nanobubbles with PMS. Microbubbles are bubbles with a diameter less than 1 mm, and their stability is much lower than that of nanobubbles. They will shrink into nanobubbles or disappear in water. During the research process, only attention is paid to whether the removal can be achieved, while ignoring whether the method can achieve long-term purification.

[0013] The present invention proposes a method for long-term water purification that only requires the addition of nano-bubbles and PMS, achieving long-term water purification without the input of external energy and chemicals. This technical solution solves the problem of difficult catalyst preparation by selecting easily available and low-cost raw materials, simplifying the preparation process or developing new and efficient catalytic materials. Moreover, through the reaction conditions, the possibility of secondary pollution is effectively reduced, ensuring the environmental friendliness of the technology. Summary of the Invention

[0014] The purpose of the present invention is to provide a sustainable purification method based on nano-bubbles to solve the problems in the prior art such as high energy consumption, inability to continuously purify, difficulty in meeting the requirements of large-scale water treatment applications, and high risk of secondary pollution in the method of activating persulfate in the background art.

[0015] To achieve the above object, the present invention is implemented by the following technical solutions: The present invention proposes a sustainable purification method based on nano-bubbles, including the following steps: Preparing a nano-bubble solution through a nano-bubble generator; Mixing the nano-bubble solution with persulfate to activate persulfate, and promoting the decomposition of persulfate on the nano-bubble interface to generate sulfate radicals; After activation, the persulfate is used for water treatment and purification.

[0016] Preferably, in the nano-bubble solution, the diameter of the nano-bubbles is less than 1 micron and the surface is negatively charged.

[0017] Preferably, when mixing, the concentration of the nano-bubble solution is 1×10 7 ~ 1×10 9 per mL.

[0018] Preferably, when mixing, the concentration of the persulfate is greater than 0.5 mM.

[0019] Preferably, the nano-bubble generator prepares the nano-bubble solution as follows: The nano-bubble generator mixes water and gas, and performs intense mixing through a high-speed shearing device, and at the same time combines the condition of rapid pressure drop to promote the nucleation of gas in the liquid, thereby generating nano-bubbles.

[0020] Preferably, the intense mixing is specifically high-intensity mixing through a high-speed shearing device, and the shear rate is controlled within the range of 1×10 4 s -1 ~ 5×10 4 s -1 or the rotation speed is controlled between 10,000 revolutions per minute and 30,000 revolutions per minute.

[0021] Preferably, the gas is one or more of oxygen, nitrogen, and air.

[0022] Preferably, the nanobubble generator includes a pump, a nanoporous membrane, and a pressure regulation system; Place the water inlet of the nanoporous membrane in the water tank. The oxygen cylinder is connected to the nanoporous membrane through a pipeline. The liquid and gas enter the pump after filtration. The pump serves as a high-speed shearing device. The pump provides power to mix oxygen and water. The mixed gas-liquid fluid undergoes a rapid pressure drop from 0.4 - 1.0 MPa to atmospheric pressure through the pressure regulation system to form a uniform nanobubble solution.

[0023] Further, the volume ratio of gas to liquid in the gas-liquid fluid is controlled at 1:10.

[0024] Further, the temperature of the gas-liquid fluid is 25°C and the pH value is 6.5 - 8.5.

[0025] Further, the pressure regulation system includes a pressure gauge, a pressure stabilizing valve, a pressure reducing device, and an outlet.

[0026] Preferably, the activated persulfate is used for water treatment and purification. The prepared nanobubble solution can exist for more than 60 days under airtight and light-proof conditions, and is used for the continuous activation of persulfate and pollutant removal. This long-term stability not only stems from the interfacial properties of the nanobubbles themselves, but also benefits from the specific preparation parameters adopted, including the control of the gas-liquid ratio (1:10), temperature (25°C), and pH value (6.5 - 8.5), thereby reducing the ionic strength and viscosity of the solution, reducing the coalescence and rupture of nanobubbles, and significantly extending the existence time of nanobubbles in water.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) Increase the generation amount of free radicals: Nanobubbles provide reaction sites and energy for the activation of PMS, greatly improving the generation efficiency of SO4 - ·, thereby enhancing the oxidative degradation ability of pollutants and improving the treatment efficiency.

[0028] (2) Strong sustainability: Nanobubbles have extremely high stability and can stably exist in water for dozens of days or even months. Their ability to continuously release oxygen and activate PMS can achieve long-term and effective environmental remediation, meeting the water treatment requirements under complex conditions, and reflecting the sustainability and reliability of the process.

[0029] (3) Low energy consumption and simple preparation process: In the present invention, the nanobubble generating device uses high-speed shearing and pressure changes to generate nanobubbles, and can efficiently activate potassium persulfate without complex equipment or high-energy-consuming methods such as light and heat, significantly reducing energy consumption and simplifying the process flow.

[0030] (4) Easy to operate: The device in the present invention is compact, easy to operate and maintain, suitable for flexible deployment in different scenarios, and has high practicability. Compared with the prior art that relies on the preparation process of complex catalytic materials, the operation steps and control difficulty are significantly simplified.

[0031] (5) Green and environmentally friendly: Compared with the traditional activation technology that requires heavy metal catalysts, the present invention avoids the use of heavy metal catalysts and eliminates the problem of secondary pollution caused by heavy metal residues, reflecting the advantages of green environmental protection, and is particularly suitable for water purification scenarios with high environmental safety requirements.

[0032] In summary, through innovative structural design and utilization of the characteristics of nanobubbles, the present invention realizes low-energy consumption, pollution-free, and sustainable green environmental remediation while improving the oxidation degradation efficiency, providing an efficient, environmentally friendly, and economical new approach for water pollution treatment. Description of the Drawings

[0033] Figure 1 is a flowchart of the sustainable purification method based on nanobubbles in the present invention; Figure 2 is a schematic diagram of the pollutant removal situation at pH = 7 for 180 minutes ( Figure 2 the pollutant in (a) is carbamazepine, Figure 2 the pollutant in (b) is phenol, Figure 2 the pollutant in (c) is bisphenol A, Figure 2 the pollutant in (d) is sulfamethoxazole); Figure 3 is a schematic diagram of the total organic carbon mineralization of pollutants at pH = 7 for 60 days; Figure 4 is a physical diagram for verifying the storage situation of nanobubbles at different times through the Tyndall effect. Detailed Embodiments

[0034] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0035] Embodiment 1: Refer to Figure 1 , the sustainable purification method based on nanobubbles includes the following steps: Step 1, prepare a nanobubble solution through a nanobubble generator.

[0036] The nano-bubble generator consists of a pressure regulation system, a pump, and a reactor. The reactor uses a nano-porous membrane. The water inlet of the nano-porous membrane is placed in a water tank filled with clean water. An oxygen cylinder is connected to the nano-porous membrane through a pipeline, and the pump provides power to mix oxygen and water. The mixed gas-liquid fluid undergoes a rapid pressure drop from 0.4 - 1.0 MPa to atmospheric pressure through the pressure regulation system, forming a uniform nano-bubble solution. The pressure regulation system includes a pressure gauge, a pressure stabilizing valve, a pressure reducing device, and an outlet. The nano-bubble solution flows into a mixing container from the outlet of the pressure regulation system for storage and standby.

[0037] This generator uses a pump to mix water and gas, and conducts intense mixing through a high-speed shearing device. At the same time, combined with the condition of rapid pressure drop, it promotes gas nucleation in the liquid, thereby generating a large number of stable nano-bubbles that can exist in water for up to several months.

[0038] Step 2: Mix the nano-bubble solution with persulfate to activate the persulfate. The persulfate is potassium peroxymonosulfate, with the molecular formula KHSO5·0.5KHSO4·0.5K2SO4 and a molecular weight of 307.38.

[0039] The stored nano-bubble solution is mixed with persulfate. Nano-bubbles have significant characteristics. A unique alkaline microenvironment is formed at their gas-water interface, where a large number of hydroxide ions (OH - )accumulate. When PMS is added to the nano-bubble solution, PMS combines with OH - at the interface through hydrogen bonding and is concentrated at the gas-water interface. The formation of this hydrogen bond effectively reduces the dissociation energy of O - O in the PMS molecule, enabling PMS to be more easily excited in the alkaline environment, thereby efficiently releasing SO4 - ·, causing the decomposition of persulfate to generate SO4 - · at the nano-bubble interface, realizing the oxidative removal of pollutants.

[0040] Step 3: After the stored nano-bubble solution is mixed with persulfate, it enters the reaction module, and the finally purified water is output from the reaction module, achieving a sustainable water treatment effect.

[0041] The nano-bubbles in the present invention have a diameter of less than 1 micron, a huge specific surface area, and a negatively charged surface. Adjacent bubbles repel each other due to the same-sex charge, avoiding coalescence. The small size results in almost the disappearance of the buoyancy effect, and the kinetic stability dominates. The gas supersaturated environment maintains a dynamic balance. These mechanisms work together, enabling the nano-bubbles to break through the classical theory prediction and stably exist in water for ten days to several months, becoming an efficient and long-lasting gas-liquid interface system, providing a potential continuous reaction site and energy source for activating persulfate, and still having a removal effect for ten days to several months.

[0042] Meanwhile, the unique microenvironment and efficient energy transfer characteristics on the surface of nanobubbles further enhance the generation efficiency of free radicals and significantly improve the degradation effect on organic pollutants in water. The whole process combines the nanobubble interface effect and the oxidation characteristics of PMS to achieve the goal of efficient and persistent removal of pollutants.

[0043] Experimental verification: In this invention, nanobubbles were used in combination with PMS to remove target pollutants, and PMS alone was used to remove target pollutants. The target pollutants were carbamazepine, phenol, bisphenol A, and sulfamethoxazole respectively.

[0044] Removal of target pollutants by nanobubbles in combination with PMS: 3 L of deionized water (resistivity 18.2 mΩ·cm) was used as the water source, oxygen was used as the gas source, the gas pressure was 60 psi, the flow rate was 300 mL / min, the water pressure in the pipe was 0.4 MPa, the temperature was 25 °C, and the water was circulated in the nanobubble generator for 5 minutes. After cooling to room temperature, 1 mM PMS and 20 μM of the target pollutant were added to 50 mL of the nanobubble solution.

[0045] Removal of target pollutants by PMS alone: 1 mM PMS and 20 μM of the target pollutant were added to 50 mL of deionized water.

[0046] Figure 2 This is the pollutant removal situation at pH = 7 for 180 minutes. Figure 2 (a), Figure 2 (b), Figure 2 (c), Figure 2 (d) show the removal situations of carbamazepine, phenol, bisphenol A, and sulfamethoxazole respectively. It can be found from Figure 2 that the removal effect of PMS alone on the four common micropollutants is not good. After adding nanobubbles, with the synergistic effect of the two, the removal effect has been significantly improved. After 180 minutes, phenol, bisphenol A, and sulfamethoxazole are almost removed, and for the difficult-to-remove carbamazepine, the removal rate has also increased by 10 times. It is proved that nanobubbles in combination with PMS can effectively improve the removal efficiency of pollutants.

[0047] From Figure 3It can be found that although the micropollutants were removed within 180 minutes, the total organic carbon (TOC) content in the solution did not decrease significantly after 180 minutes, indicating that the organic matter was not mineralized, that is, hydrolyzed into carbon dioxide and water, but existed in the form of intermediate products, which may pose certain health risks. Continuous TOC monitoring of the four solutions was continued, and the study found that without the addition of energy and drugs, phenol, bisphenol A and aniline could reduce TOC by 90% after two weeks to achieve water purification; carbamazepine and sulfamethoxazole, which have more complex structures, also achieved more than 80% removal after 30 days; the natural organic matter solution simulating real water bodies continued to reduce TOC within 60 days, indicating that nanobubbles in conjunction with PMS can achieve long-term water purification, breaking the general method's demand for energy, medicine bottles and continuity. And through the Tyndall effect, it was verified that the nanobubbles still existed after 60 days of storage, such as Figure 4 shown.

[0048] The above description is only used to help understand the method of the present invention and its core essence, but the protection scope of the present invention is not limited thereto. For those skilled in the art in the art, equivalent replacement or change according to the technical solution and inventive concept of the present invention within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A sustainable purification method based on nanobubbles, characterized in that, It includes the following steps: Prepare a nano-bubble solution through a nano-bubble generator; the nano-bubble generator mixes water and gas, and conducts intense mixing through a high-speed shearing device, and at the same time combines the condition of a rapid pressure drop from 0.4~1.0 MPa to atmospheric pressure to promote gas nucleation in the liquid, thereby generating nano-bubbles; the volume ratio of the mixed gas and liquid is controlled at 1:10, the temperature is 25°C, and the pH value is 6.5~8.5; In the nano-bubble solution, the diameter of the nano-bubbles is less than 1 micron, and the surface is negatively charged; Mix the nano-bubble solution with persulfate to activate the persulfate, and promote the decomposition of persulfate to generate sulfate radicals at the nano-bubble interface; After activation, the persulfate is used for water treatment and purification.

2. The sustainable purification method based on nanobubbles according to claim 1, wherein The concentration of the nano-bubble solution is 1×10 7 ~ 1×10 9 per mL.

3. The sustainability purification method based on nano-bubbles according to claim 1, wherein When mixing, the concentration of the persulfate is greater than 0.5 mM.

4. The sustainability purification method based on nanobubbles according to claim 1, characterized in that The nano-bubble generator prepares the nano-bubble solution as follows: Intense mixing specifically refers to high-intensity mixing through a high-speed shearing device, with the shear rate controlled within the range of 1×10 4 s -1 ~ 5×10 4 s -1 or the rotation speed is controlled between 10,000 revolutions per minute and 30,000 revolutions per minute.

5. The sustainable purification method based on nanobubbles according to claim 4, characterized in that, The gas is one or more of oxygen, nitrogen, and air.

6. The sustainability purification method based on nanobubbles according to claim 5, characterized in that, The nano-bubble generator includes a pump, a nano-porous membrane, and a pressure regulation system; Place the water inlet of the nano-porous membrane in the water tank, connect the oxygen cylinder to the nano-porous membrane through a pipeline, filter the liquid and gas and then enter the pump. The pump serves as a high-speed shearing device, and the pump provides power to mix oxygen and water. The mixed gas-liquid fluid realizes a rapid pressure drop from 0.4~1.0 MPa to atmospheric pressure through the pressure regulation system to form a uniform nano-bubble solution.

7. The sustainability purification method based on nano-bubbles according to any one of claims 1-6, characterized in that, After activation, the persulfate is used for water treatment and purification. The prepared nano-bubble solution can exist for more than 60 days under airtight and light-shielded conditions, and is used for the continuous activation of persulfate and pollutant removal.

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