A method for selectively removing nitrate from wastewater based on ionizing radiation

Abstract

The application belongs to the technical field of environmental pollution wastewater treatment, and particularly relates to a method for selectively removing nitrate in wastewater based on ionizing radiation. The application adjusts the pH of wastewater and adds formate, utilizes the reaction of formate with hydroxyl radicals (•OH) and hydrogen radicals (•H) in the wastewater to be treated to generate carbon dioxide radicals (CO2 ‑ ), and utilizes the carbon dioxide radicals to selectively reduce nitrate (NO3 ‑ ) into nitrogen, so as to solve the problem of low efficiency of selective reduction of nitrate by existing ionizing radiation, and how to improve the efficiency of selective reduction of nitrate by ionizing radiation is a key problem in the application of the technology in wastewater treatment.

Description

Technical Field

[0001] This application belongs to the field of environmental pollution wastewater treatment technology, specifically relating to a method for selectively removing nitrate from wastewater based on ionizing radiation. Background Technology

[0002] With the intensification of industrial activities, large amounts of nitrogen-containing wastewater are being discharged into the environment, especially wastewater containing high concentrations of nitrate (NO3). - Nitrate wastewater poses a serious threat to aquatic ecosystems and human health. Currently, commonly used nitrate removal technologies mainly include biological denitrification, ion exchange, reverse osmosis, and chemical reduction. However, these methods have many limitations in practical applications, such as high requirements for water quality conditions, high operating costs, or the generation of secondary pollution.

[0003] Ionizing irradiation is an advanced oxidation / reduction technology that generates a series of highly oxidizing and reducing reactive species in water through high-energy irradiation, such as hydroxyl radicals (•OH), hydrogen radicals (•H), and hydrated electrons (e). aq Ionizing irradiation can effectively degrade recalcitrant organic pollutants. However, current ionizing irradiation methods have low selective reduction efficiency for nitrate. How to improve the selective reduction efficiency of ionizing irradiation for nitrate is a key issue in the current application of this technology in wastewater treatment. Summary of the Invention

[0004] In view of this, this application provides a method for selectively removing nitrate from wastewater based on ionizing radiation. This method involves adjusting the pH of the wastewater and adding formate, which reacts with hydroxyl radicals (•OH) and hydrogen radicals (•H) in the wastewater to generate carbon dioxide radicals (CO2•). - ), using carbon dioxide free radicals to remove nitrate (NO3) - The selective reduction of nitrate to nitrogen gas is a key issue in the current application of this technology in wastewater treatment, which addresses the low selective reduction efficiency of nitrate by existing ionizing irradiation.

[0005] This application provides a method for selectively removing nitrate from wastewater based on ionizing radiation, the method comprising: Step S1: Adjust the pH of the wastewater containing nitrate to 6.5-8.5 to obtain the pH-adjusted wastewater. Step S2: Add formate to the pH-adjusted wastewater to make the formate concentration 0.1 mmol / L to 10 mmol / L, so as to obtain wastewater with added formate. Step S3: Irradiate the wastewater containing formate using an ionizing radiation source, so that the formate reacts with •OH and •H in the wastewater to generate carbon dioxide free radicals, utilizing CO2• - Nitrate ions are selectively reduced to nitrogen gas.

[0006] In one specific embodiment of this application, the relationship between the irradiation dose of the ionizing radiation source and the formate concentration is that 1 kGy corresponds to a formate concentration of 0.1 mM to 0.5 mM.

[0007] In one specific embodiment of this application, the relationship between the irradiation dose of the ionizing radiation source and the formate concentration is that 1 kGy corresponds to a formate concentration of 0.3 mM.

[0008] In one specific embodiment of this application, the irradiation dose of the ionizing radiation source ranges from 0.1 to 30 kGy.

[0009] In one specific embodiment of this application, the formate is sodium formate.

[0010] In one specific embodiment of this application, the formate is potassium formate.

[0011] In one specific embodiment of this application, the ionizing radiation source includes gamma rays, X-rays, or an electron beam.

[0012] The beneficial effects of the technical solution in this application are as follows: Highly selective reduction: CO2•) for NO3 - It has excellent reduction capabilities and low reactivity to other coexisting pollutants, thus achieving selective reduction in complex water conditions.

[0013] Strong anti-interference ability: Compared with hydrated electrons, CO2• - It is not easily quenched by the matrix in water, thus ensuring the reduction efficiency in actual wastewater systems.

[0014] Synergistic removal of pollutants: in environments containing NO3 - In wastewater containing both organic and non-organic pollutants, this system can remove both types of pollutants simultaneously, simplifying the treatment process.

[0015] Green and environmentally friendly: This method does not introduce secondary pollution. Formate is converted into CO2 after the reaction, leaving no residual toxic byproducts. Attached Figure Description

[0016] Figure 1 The diagram shown is a flowchart illustrating a method for selectively removing nitrate from wastewater based on ionizing radiation, according to an embodiment of this application. Detailed Implementation

[0017] Careful research revealed that in complex water bodies, hydrated electrons are easily quenched by the matrix, significantly reducing the selective reduction capacity of existing ionizing irradiation for nitrate. Based on this finding, this application provides a method for selectively removing nitrate from wastewater using ionizing irradiation. This method utilizes the reaction of formate with HO• or H• during ionizing irradiation to generate CO2•. - Through CO2• - Its high selectivity for reducing nitrate ions enables efficient removal of nitrate ions from complex wastewater.

[0018] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0019] At least one embodiment of this application provides a method for selectively removing nitrate from wastewater based on ionizing radiation, see reference. Figure 1 The method for selectively removing nitrate from wastewater based on ionizing radiation includes the following steps S1 to S3.

[0020] Step S1: Adjust the pH of the wastewater containing nitrate to 6.5-8.5 to obtain the pH-adjusted wastewater.

[0021] Specifically, the wastewater to be treated is pretreated to adjust its pH to neutral to slightly alkaline (preferably in the range of 6.5 to 8.5).

[0022] Step S2: Add formate to the wastewater to be treated after pH adjustment, so that the concentration of formate is 0.1 mmol / L to 10 mmol / L, so as to obtain wastewater to be treated with added formate.

[0023] In at least one embodiment of this application, the formate is sodium formate or potassium formate.

[0024] Step S3: Irradiate the wastewater containing formate using an ionizing radiation source, so that the formate reacts with •OH and •H in the wastewater to generate CO2. - , using CO2• - NO3 - It is selectively reduced to nitrogen gas.

[0025] •OH + HCOO - → CO2• - + H2O •H + HCOO - → CO2•- + H2↑ Specifically, during ionization irradiation, formate reacts with •OH and •H free radicals to generate CO2• - This free radical has a high reducing power and can reduce NO3-. - It is selectively reduced to nitrogen gas.

[0026] Compared with the prior art, the embodiments of this application have the following advantages: Highly selective reduction: carbon dioxide free radicals (CO2• - ) for nitrate (NO3) - It has excellent reduction ability and low reactivity to other coexisting pollutants, thus achieving selective reduction in complex water conditions.

[0027] Strong anti-interference ability: Compared with hydrated electrons, CO2• - Free radicals are not easily quenched by the matrix in water, ensuring reduction efficiency in actual wastewater systems. Specifically, although hydrated electrons do not react with formate, they readily undergo quenching reactions with the simultaneously generated •OH in irradiated systems, thus reducing their effective concentration. Upon adding formate to the system, formate preferentially reacts with •OH and •H to generate CO2• - This significantly reduces the instantaneous concentration of •OH in the system. The reduction in •OH decreases, on the one hand, lessens the quenching effect of •OH on hydrated electrons, increasing the concentration of effective hydrated electrons available for reduction reactions in the system; on the other hand, it generates more stable CO2• through free radical conversion reactions. - This increases the total concentration of reducing active species in the system. Under the above synergistic effect, hydrated electrons and CO2• - Jointly participate in NO3 - The reduction reaction, in which CO2• - Because it is not easily quenched by the matrix in water, it plays a major role in the selective reduction of nitrate to nitrogen in actual wastewater systems, thus ensuring the overall reduction efficiency.

[0028] Synergistic removal of pollutants: in environments containing NO3 - In wastewater containing both organic and non-organic pollutants, this system can remove both types of pollutants simultaneously, simplifying the treatment process.

[0029] Green and environmentally friendly: This method does not introduce secondary pollution. Formate is converted into CO2 after the reaction, leaving no residual toxic byproducts.

[0030] In at least one embodiment of this application, the ionizing radiation source includes, but is not limited to, gamma rays, X-rays, or electron beams.

[0031] In at least one embodiment of this application, the relationship between the irradiation dose of the ionizing radiation source and the formate concentration is that 1 kGy corresponds to a formate concentration of 0.1 mM to 0.5 mM.

[0032] Choosing a range for formate concentration offers the following technical advantages: when the formate concentration is below the aforementioned range, the reaction between formate and hydroxyl radicals (•OH) in the system is less dominant, the quenching effect of hydroxyl radicals on hydrated electrons is not significantly weakened, and the generated carbon dioxide radicals (CO2•OH) are less affected. - Insufficient quantity leads to a low concentration of effective reducing active species in the system, which is not conducive to the efficient reduction of nitrate.

[0033] When the formate concentration exceeds the above range, an excess of carbon dioxide free radicals (CO2•) will be generated in the system. - Excessive CO2 - It is prone to free radical self-reaction to generate stable products such as oxalic acid, thereby consuming reducing active free radicals and weakening the reducing effect of carbon dioxide free radicals on nitrate, which is not conducive to improving the overall reduction efficiency.

[0034] Therefore, controlling the formate concentration at an irradiation dose of 1 kGy within the range of 0.1 mM to 0.5 mM can achieve a good balance between inhibiting the adverse reaction of hydroxyl radicals, increasing the effective concentration of reducing radicals, and avoiding excessive consumption of radicals, thereby achieving efficient and selective reduction of nitrate.

[0035] In at least one embodiment of this application, the relationship between the irradiation dose of the ionizing radiation source and the formate concentration is that 1 kGy corresponds to a formate concentration of 0.3 mM.

[0036] For example, when the irradiation dose is 1 kGy, a formate concentration of 0.3 mM ensures that the reaction between formate and •OH in the system is dominant, effectively reducing the instantaneous concentration of •OH, thereby reducing the quenching effect of •OH on hydrated electrons and improving the utilization efficiency of available hydrated electrons in the system; at the same time, this concentration level can promote the generation of an appropriate amount of CO2• - This significantly increases the overall concentration of reducing active species in the system. If the formate concentration is below 0.3 mM, the quenching effect of •OH is insufficient, and the generated CO2• - Limited quantity hinders efficient nitrate reduction; if the formate concentration exceeds 0.3 mM, it may lead to excessive generation of carbon dioxide free radicals in the system, resulting in excessive CO2• - It is prone to self-reaction to generate stable products such as oxalic acid, thereby consuming reducing free radicals and weakening its reduction effect on nitrate.

[0037] In at least one embodiment of this application, the dose range of the ionizing radiation source is 0.1 to 30 kGy.

[0038] In at least one embodiment of this application, the concentration range of nitrate in the wastewater to be treated is (0 mg / L, 50 mg / L).

[0039] Example 1 Nitrate wastewater was prepared with an initial pH of 7.0 and a nitrate concentration of 20 mg / L. 0.75 mM formate was added, and then the water was irradiated with 5 kGy. After treatment, the nitrate concentration in the water was reduced to 4.4 mg / L, and the nitrogen produced contained 63% of the total nitrogen content.

[0040] Comparative Example 1: Nitrate wastewater was prepared with an initial pH of 7.0 and a nitrate concentration of 20 mg / L. After irradiation with 5 kGy, the nitrate concentration in the water was reduced to 17.9 mg / L, and the nitrogen content in the generated nitrogen gas accounted for 9.7% of the total nitrogen content.

[0041] By comparing Example 1 and Comparative Example 1, it can be seen that the addition of formate can effectively enhance the ability of ionizing radiation to treat nitrate in wastewater.

[0042] Example 2 Wastewater containing nitrate and phenol was prepared with an initial pH of 7.0, a nitrate concentration of 20 mg / L, and a phenol concentration of 10 mg / L. 0.75 mM formate was added, and then the solution was irradiated with 5 kGy. After treatment, the nitrate concentration in the water decreased to 7.8 mg / L and the phenol concentration decreased to 1.5 mg / L.

[0043] Comparative Example 2: Wastewater containing nitrate and phenol was prepared with an initial pH of 7.0, a nitrate concentration of 20 mg / L, and a phenol concentration of 10 mg / L. After irradiation with 5 kGy, the nitrate concentration in the water was reduced to 13.9 mg / L and the phenol concentration was reduced to 0.2 mg / L.

[0044] Comparative Example 2 and Comparative Example 2 show that adding formate can promote the removal of nitrate when nitrate and organic pollutants are present simultaneously. Although the effect of ionizing irradiation on phenol decreases compared to the absence of formate, the effect on nitrate removal is enhanced.

[0045] Comparative Example 3: Nitrate wastewater was prepared with an initial pH of 7.0 and a nitrate concentration of 20 mg / L. 0.75 mM formic acid (non-formate) was added, and then the water was irradiated with 5 kGy. After treatment, the nitrate concentration in the water was reduced to 9.4 mg / L, and the nitrogen content in the produced nitrogen gas accounted for 37% of the total nitrogen content.

[0046] It should be noted that the combination of the technical features in the embodiments of this application is not limited to the combination methods described in the embodiments of this application or the combination methods described in specific embodiments. All technical features described in this application can be freely combined or combined in any way, unless they contradict each other.

[0047] As indicated in this application and claims, unless the context clearly indicates otherwise, the words "a," "an," and / or "the" do not specifically refer to the singular and may also include the plural. Generally speaking, the term "comprising" only indicates that it includes the explicitly identified steps and elements, which do not constitute an exclusive list, and the method or apparatus may also include other steps or elements.

[0048] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications or equivalent substitutions made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for selectively removing nitrate from wastewater based on ionizing radiation, characterized in that, include: Step S1: Adjust the pH of the wastewater containing nitrate to 6.5-8.5 to obtain the pH-adjusted wastewater. Step S2: Add formate to the pH-adjusted wastewater to make the formate concentration 0.1 mmol / L to 10 mmol / L, so as to obtain wastewater with added formate. Step S3: Irradiate the wastewater containing formate using an ionizing radiation source so that the formate reacts with hydroxyl radicals and hydrogen radicals in the wastewater to generate carbon dioxide radicals, and use the carbon dioxide radicals to selectively reduce nitrate to nitrogen.

2. The method according to claim 1, characterized in that, The relationship between the irradiation dose of the ionizing radiation source and the formate concentration is that 1 kGy corresponds to a formate concentration of 0.1 mM to 0.5 mM.

3. The method according to claim 2, characterized in that, The relationship between the irradiation dose of the ionizing radiation source and the formate concentration is that 1 kGy corresponds to a formate concentration of 0.3 mM.

4. The method according to claim 1, characterized in that, The irradiation dose range of the ionizing radiation source is 0.1–30 kGy.

5. The method according to any one of claims 1 to 4, characterized in that, Formate is sodium formate.

6. The method according to any one of claims 1 to 4, characterized in that, Formate is potassium formate.

7. The method according to any one of claims 1 to 4, characterized in that, Ionizing radiation sources include gamma rays, X-rays, or electron beams.

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