Method for removing pollutants in water body by means of electro-activated sulfite

Abstract

Disclosed in the present invention is a method for removing pollutants in a water body by means of an electro-activated sulfite. The method comprises: adding a sulfite solution to a water body containing pollutants, then applying a direct current onto same, and continuously stirring same to remove organic pollutants and / or inorganic pollutants in the water body. By means of the method, organic pollutants and / or inorganic pollutants in a water body can be removed according to requirements.

Description

A method for removing water pollutants by electrically activating sulfite Technical Field

[0001] The invention belongs to the technical field of water pollution remediation, and particularly relates to a method for removing water pollutants using electrically activated sulfite. Background Art

[0002] With economic development and social progress, a wide variety of new pollutants are frequently detected in water bodies, posing a serious threat to human health. On the one hand, organic pollutants such as environmental endocrine disruptors, pharmaceuticals and personal care products, and pesticides are highly toxic and persistent in the environment, and are difficult to remove using traditional water treatment processes. On the other hand, inorganic pollutants such as bromate, chlorite, and heavy metal ions are highly mutagenic and carcinogenic. In addition, with the development of industry, complex water pollution is becoming increasingly common. For example, in water bodies after oxidation or disinfection, there is complex pollution of organic pollutants and halogenated byproducts such as chlorite and bromate; in industrial wastewater from electroplating, smelting, leather making, printing and dyeing, and pharmaceutical manufacturing, there is complex pollution of hexavalent chromium and organic pollutants; and in flue gas desulfurization wastewater, there is complex pollution of sulfite, heavy metal ions, and organic pollutants.

[0003] Advanced oxidation technologies, which generate highly oxidizing free radicals during the reaction process, can effectively oxidize and mineralize difficult-to-degrade organic pollutants. Advanced reduction technologies, which generate reducing active substances, can effectively reduce and dehalogenate inorganic pollutants, achieving high removal efficiencies for inorganic pollutants. While these advanced oxidation and reduction technologies offer high oxidation or reduction removal rates for single pollutants, they struggle to simultaneously remove multiple pollutants in complexly contaminated water bodies.

[0004] Therefore, developing a new technology that can both oxidize organic pollutants and reduce inorganic pollutants is more appropriate for addressing the increasingly severe water pollution situation. Activated sulfite technology can simultaneously generate oxidizing and reducing active species, making it suitable for both advanced oxidation and reduction processes, and holds great promise for its application in water remediation.

[0005] When sulfite is activated as an advanced oxidation process, the oxidative active species (SO4· - , SO5· - , HO·) can effectively oxidize and mineralize organic matter. Compared with persulfate, sulfite has the advantages of being less toxic and expensive, and does not produce halogenated byproducts.

[0006] When sulfite is activated as an advanced reduction process, the reducing active species produced include SO3· - ,eaq- and H,· can be effectively reduced and dehalogenated.

[0007] Oxygen concentration is the key difference between sulfite advanced reduction and advanced oxidation processes. Traditional sulfite activation technologies (UV activation, transition metal ion activation, high-valent oxygen-containing metal salts, thermal activation) require additional oxygen when used as advanced oxidation processes; when used as advanced reduction processes, a strictly controlled oxygen-free environment is required. These technologies generally can only be used for oxidation or reduction in a unidirectional manner, and are unable to simultaneously oxidize and reduce multiple pollutants. Furthermore, UV activation and thermal activation consume significant energy, and the metal toxicity of metal ions introduced by transition metal ion and high-valent oxygen-containing metal salt activation can cause secondary pollution.

[0008] Summary of the Invention

[0009] The present invention provides a method for removing water pollutants using electro-activated sulfite. The method can remove organic pollutants and / or inorganic pollutants in water as required.

[0010] The present invention provides a method for removing water pollutants by electro-activating sulfite, comprising: adding a sulfite solution to the water containing the pollutants, then passing direct current, and continuously stirring to remove organic pollution and / or inorganic pollutants in the water.

[0011] Furthermore, when the DC current is 100-300 mA and the concentration of the sulfite solution is 2-4 mM, the rate of removing organic pollutants in the water is 0.031-0.17 min -1 .

[0012] Under the conditions of passing a suitable current and a suitable concentration of sulfite solution, the electrochemical oxidation of sulfite and the rate of generating oxygen are balanced, SO4· - The production rate of sulfite is high, and the rate of oxidizing organic pollutants is fast. Therefore, the main purpose of this process is to remove organic pollutants. When the concentration of sulfite solution is too high, the oxygen evolution rate is slow, the conversion rate of sulfoxide free radicals is slow, and SO4· - The production rate is slow. On the other hand, too much sulfite will quench SO4· - , which greatly reduces the oxidation efficiency of organic pollutants.

[0013] Further preferably, before adding the sulfite solution to the pollutant-containing water, the pH of the pollutant-containing water is adjusted to be higher than 7. In the electric field environment, the alkaline conditions can better oxidize the organic pollutants to remove the organic pollutants, and the pH of the water is regulated by adding inorganic bases. Under alkaline conditions, the electro-activated sulfite produces SO3· -The rate of production (Formula (1)) is faster than the rate of production of HSO3· under acidic conditions (Formula (2)). In addition, the oxygen evolution potential is lower, the rate of production of oxygen (Formula (3)) is faster than that under acidic conditions (Formula (4)), and the rate of conversion of sulfoxide radicals (Formula (5-13)) is faster. Therefore, SO4· - The production rate of SO3 (Formula (11)) and the production rate of HO· (Formula (13)) are faster. 2- -e - →SO3 - (E(SO3· - / SO3 2- =0.63V) (1) HSO3 - -e - →HSO3·(E(HSO3· / HSO3 - =0.84V) (2) 4OH - -4e - →O2+2H2O(E(O2 / OH - =0.401V) (3) 2H2O-4e - →O2+4H + (E(O2 / OH - =1.229V) (4) SO3· - -e - +2OH - →SO4 2- +H2O(K SO3·- =4.38cm / s) (5) HSO3·-e - +H2O→SO4 2- +3H + (K HSO3· =2.83cm / s) (6) SO3· - +O2→SO5 - (k=2.5×10 9 M -1 s -1 ) (7) HSO3·+O2→HSO5·(k=1.1×10 9 M -1 s -1 ) (8) SO5· - +SO3 2- →SO3 - +SO52- (k=1.0×10 8 M -1 s -1 ) (9) HSO5·+HSO3 - →HSO3·+HSO5 - (k=3.0×10 7 M -1 s -1 ) (10) SO5· - +SO3 2- →SO4 - +SO4 2- (k=5.0×10 8 M -1 s -1 ) (11) HSO5·+HSO3·→SO4· - +SO4 2- +2H + (k=6.0×10 7 M -1 s -1 ) (12) SO4· - +OH - →SO4 2- +OH·(k=6.0×10 7 M -1 s -1 ) (13)

[0014] Furthermore, when the DC current is 20-40 mA and the concentration of the sulfite solution is 2-6 mM, the rate of removing inorganic pollutants in the water is 0.023-0.12 min -1 .

[0015] Under the conditions of passing a suitable current and a suitable concentration of sulfite solution, the electrode reaction is mainly oxidized sulfite, and the oxygen evolution reaction is almost completely inhibited. - The higher the concentration of sulfite solution, the faster the reduction rate of inorganic pollutants. Therefore, the main purpose of this process is to remove inorganic pollutants. And the energy consumption is low. When the concentration of sulfite solution is too high, HSO3· / SO3· - The production rate will not be significantly improved because the limit of HSO3· / SO3· - The rate of generation is determined by the current density.

[0016] It is further preferred that the pH of the pollutant-containing water body is adjusted to be lower than 6.5 before adding the sulfite solution to the pollutant-containing water body. In an electric field environment, the inorganic pollutants can be better reduced by acidic conditions to remove the inorganic pollutants, and the pH of the water body is regulated by adding inorganic acid. Under acidic conditions, the rate of oxygen generation is low (Formula (4)). In addition, the electrochemical oxidation rate (Formula (6)) and oxygen oxidation rate (Formula (8)) of HSO3· are both higher than those of SO3·. - The electrochemical oxidation rate (Equation (5)) and oxygen oxidation rate (Equation (7)) of HSO3 are low. Therefore, the concentration of HSO3· is higher under acidic conditions, and the reduction rate of inorganic pollutants is faster.

[0017] Furthermore, when the DC current is 60-100 mA and the concentration of the sulfite solution is 2-4 mM, the rate of removing organic pollutants in the water is 0.015-0.028 min -1 The rate of removing inorganic pollutants from water is 0.019-0.077min -1 .

[0018] By passing a current of appropriate size and a sulfurous acid solution of appropriate concentration, a certain concentration of reducing free radicals and oxidizing free radicals will coexist in the system, so that the reducing free radicals and oxidizing free radicals reach a balance, thereby achieving the effect of synchronous redox.

[0019] Further preferably, before adding the sulfite solution to the pollutant-containing water, the pH of the pollutant-containing water is adjusted to 6-9. Under neutral conditions, the concentrations of sulfite and bisulfite in the water are equivalent (Formula (14)), which can achieve simultaneous oxidation of organic pollutants and reduction of inorganic pollutants. Excessive acidity or alkalinity in the water will destroy the equilibrium state of sulfite and bisulfite concentrations, thereby causing the oxidation rate of organic pollutants to be too low or the reduction rate of inorganic pollutants to be too low. SO3 2- +H + →HSO3 - (pKa=7.18) (14)

[0020] Furthermore, the stirring rate is 400-800 rpm. With an appropriate stirring rate, the reducing free radicals and the oxidizing phase free radicals can be better transferred to the electrode, thereby enabling better oxidation and / or reduction reactions.

[0021] Furthermore, the organic pollutants include any one or more of antibiotics, pesticides, and endocrine disruptors. Furthermore, the organic pollutants are any one or more of carbamazepine, bisphenol A, metronidazole, propranolol, and atrazine.

[0022] Furthermore, the inorganic pollutants are any one or more of chlorite, chlorate, bromate, and dichromate.

[0023] Furthermore, the sulfite is sodium sulfite. The electrolyte solution used in the electro-activated sulfite system is sodium sulfate and sodium sulfite. When the water treated by the method has a limited value for sulfate concentration, there is no need to add additional electrolyte sodium sulfate.

[0024] Furthermore, an electrochemical reactor is formed by inserting a cathode and anode electrodes into the pollutant-containing water to pass direct current into the pollutant-containing water. Both the cathode and anode electrodes are titanium-based ruthenium-iridium mixed metal oxide electrodes. These electrodes have low sulfite oxidation potential and oxygen evolution potential, resulting in low power consumption.

[0025] The principle of the present invention is that sulfite loses an electron at the anode and is oxidized to generate sulfite radicals (Formula (1-2)), and an oxygen evolution reaction occurs at the same time (Formula (3-4)).

[0026] Under anoxic conditions, HSO3· / SO3· - (E 0 =-2.47V) to reduce inorganic pollutants.

[0027] Under aerobic conditions, SO4· - (Formula (11-12))(E 0 =2.5-3.1V) and HO·(Formula (13))(E 0 =2.8V) to oxidize new organic pollutants.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] (1) When the electro-activated sulfite system is used as an advanced oxidation method to remove organic pollutants, it can avoid the formation of halogenated intermediates, overcoming a major drawback of the advanced oxidation process.

[0030] (2) When the electro-activated sulfite system is used as an advanced reduction method to reduce inorganic pollutants, the applied current density is low and the power consumption is low.

[0031] (3) When the electro-activated sulfite system removes new pollutants from water, the remaining sulfite is easily oxidized at the anode to generate non-toxic sulfate ions, which will not cause secondary pollution to the water.

[0032] (4) By controlling the concentrations of different sulfoxide radicals, the electro-activated sulfite system can achieve simultaneous redox removal of multiple pollutants, which is more in line with the increasingly severe water pollution situation. For example, after chlorine and chlorine dioxide disinfection, the electro-activated sulfite system can be used to remove the disinfection byproduct chlorite and residual chlorine dioxide while efficiently oxidizing new chlorine-resistant pollutants. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] FIG1 is a fitting curve diagram of the concentration and time during the degradation of carbamazepine by the electro-activated sulfite system provided in Example 1;

[0034] FIG2 is a graph showing the oxidation fitting curves of sulfite provided in Example 1 and Comparative Example 1;

[0035] FIG3 is a fitted curve diagram of the concentrations of bromate and bromide ions versus time during the degradation of bromate by the electro-activated sulfite system provided in Example 2 and Comparative Example 2;

[0036] FIG4 is a fitting curve diagram of the concentrations of chlorite, chloride ions, and carbamazepine versus time during the degradation of chlorite and carbamazepine by the electro-activated sulfite system provided in Example 3. DETAILED DESCRIPTION

[0037] The present invention is further described in detail below with reference to specific implementation examples, but the protection scope of the present invention is not limited to the contents described above.

[0038] Example 1

[0039] The electro-activated sulfite system provided in Example 1 is used for oxidative degradation of carbamazepine, and the specific steps are as follows:

[0040] First, add 10mM sodium sulfate to the reactor, then add 5uM carbamazepine solution to the reactor, and adjust the pH value of the water to be treated to 9 with dilute sodium hydroxide and sulfuric acid. Then add 2mM sodium sulfite solution pre-adjusted to pH 9 to the water body, and the total volume of the system is 100ml. Select two 2×4cm titanium-based ruthenium iridium oxide electrodes as cathode and anode, and immerse the two electrodes (with a spacing of 1.5cm) in 100mL electrolyte solution to form a single-chamber electrolytic cell. Use a DC regulated power supply to set a constant current of 240mA (i.e., a current density of 150A / m 2 ), and the reaction temperature was adjusted to 25° C. using a water bath. During the reaction, water samples were taken at different reaction time points to determine the residual concentration of carbamazepine in the water, and degradation curves of carbamazepine under different reaction time conditions were drawn.

[0041] As shown in Figure 1(a), the removal efficiency of carbamazepine by sulfite and electrochemical oxidation alone is extremely low, while the electroactivated sulfite system effectively removes carbamazepine. Within 10 minutes, the removal rate of carbamazepine reaches over 80%, and all sulfite (Figure 2(a)) is simultaneously oxidized to sulfate. This demonstrates that the electroactivated sulfite system can rapidly degrade organic pollutants, and the generated sulfate does not cause secondary water pollution.

[0042] Comparative Example 1

[0043] The electro-activated sulfite system provided in Comparative Example 1 is used to oxidatively degrade carbamazepine, and the specific steps are as follows:

[0044] First, add 10mM sodium sulfate to the reactor, then add 5uM carbamazepine solution to the reactor, and adjust the pH value of the water to be treated to 6 with dilute sodium hydroxide and sulfuric acid. Then add 5mM sodium bisulfite solution that has been pre-adjusted to pH 6 to the water body, and the total volume of the system is 100ml. Select two 2×4cm titanium-based ruthenium iridium oxide electrodes as cathode and anode, and immerse the two electrodes (with a spacing of 1.5cm) in 100mL of electrolyte solution to form a single-chamber electrolytic cell. Use a DC regulated power supply to set a constant current of 60mA (i.e., a current density of 37.5A / m 2 ), and the reaction temperature was adjusted to 25° C. using a water bath. During the reaction, water samples were taken at different reaction time points to determine the residual concentration of carbamazepine in the water, and degradation curves of carbamazepine under different reaction time conditions were drawn.

[0045] As shown in Figure 1(b), under acidic conditions, low current density, and high bisulfite concentration, the removal rate of carbamazepine within 10 minutes is only 12%, which is much lower than the removal rate of carbamazepine in Example 1. The oxidation rate of sulfite is only 18% (Figure 2(b)), which is much lower than the oxidation rate of sulfite in Example 1. On the one hand, under acidic conditions, the generation rate of HSO3· in the electroactivated bisulfite system is low. On the other hand, since the current density is low at this time, the bisulfite concentration is too high, the oxygen generation rate is low, and the conversion rate of sulfoxide free radicals is low, resulting in the generation of SO4· - Therefore, the oxidation rate of bisulfite and the degradation rate of organic pollutants are significantly lower than those in Example 1.

[0046] Example 2

[0047] The electro-activated sulfite system provided in Example 2 is used to reduce bromate, and the specific steps are as follows:

[0048] First, add 1 mg / L bromate solution to the reactor, and adjust the pH value of the water to be treated to 6 with dilute sodium hydroxide and sulfuric acid. Select two 2×4 cm titanium-based ruthenium iridium oxide electrodes as cathode and anode, and immerse the two electrodes (with a spacing of 1.5 cm) in 100 mL of electrolyte solution to form a single-chamber electrolytic cell. Then add a sodium bisulfite solution with a concentration of 2 mM and pre-adjusted to pH 6 to the reactor, and the total volume of the system is 100 ml. Direct current is then applied to start the reduction reaction. Use a DC regulated power supply to set a constant current of 30 mA (i.e., a current density of 18.75 A / m 2 ), and the reaction temperature was adjusted to 25°C using a water bath. During the reaction, water samples were taken at different reaction time points to determine the residual concentration of bromate in the water and the concentration of bromide ions generated by the reduction. Bromate reduction curves were then plotted under different reaction time conditions.

[0049] As shown in Figure 3(a), compared to using bisulfite alone to reduce bromate, the electro-activated sulfite system significantly improves the degradation rate of bromate, degrading more than 99% of bromate within 30 minutes. The remaining bromate concentration is 7 μg / L, meeting the limit requirement of 10 μg / L in the "Sanitary Standard for Drinking Water (GB5749-2022)". When this method is used to reduce bromate in pre-ozonated water, no additional electrolyte is required. Using sulfite and bromate as electrolytes, bromate reduction can be achieved. The remaining sulfite can be removed by electrochemical oxidation, and the sulfate ion concentration in the system is approximately 250 mg / L, meeting the limit requirement of 250 mg / L in the "Sanitary Standard for Drinking Water (GB5749-2022)".

[0050] Comparative Example 2

[0051] The electro-activated sulfite system provided in Comparative Example 2 is used to reduce bromate, and the specific steps are as follows:

[0052] First, add 1 mg / L bromate solution to the reactor, and adjust the pH value of the water to be treated to 10 with dilute sodium hydroxide and sulfuric acid. Select two 2×4 cm titanium-based ruthenium iridium oxide electrodes as cathode and anode, and immerse the two electrodes (with a spacing of 1.5 cm) in 100 mL of electrolyte solution to form a single-chamber electrolytic cell. Then add a sodium bisulfite solution with a concentration of 1 mM and pre-adjusted to pH 10 to the reactor, and the total volume of the system is 100 ml. Direct current is then applied to start the reduction reaction. Use a DC regulated power supply to set a constant current of 60 mA (i.e., a current density of 37.5 A / m 2 ), and the reaction temperature was adjusted to 25°C using a water bath. During the reaction, water samples were taken at different reaction time points to determine the residual concentration of bromate in the water and the concentration of bromide ions generated by the reduction. Bromate reduction curves were then plotted under different reaction time conditions.

[0053] As shown in Figure 3(b), under alkaline conditions, high current density, and low sulfite concentration, the bromate removal rate within 30 minutes is only 5%, which is much lower than the bromate removal rate in Example 2. On the one hand, under alkaline conditions, the SO3· - On the other hand, due to the high current density and low sulfite concentration, the oxygen generation rate is fast, SO3· - Almost all of it is captured by oxygen and cannot be used for the reduction of bromate.

[0054] Example 3

[0055] The electro-activated sulfite system provided in Example 3 simultaneously reduces chlorite and oxidizes carbamazepine, and the specific steps are as follows:

[0056] First, add a 2mg / L chlorite solution and a 2uM carbamazepine solution to the reactor, and adjust the pH value of the water to be treated to 7 with dilute sodium hydroxide and sulfuric acid. Select two 2×4cm titanium-based ruthenium iridium oxide electrodes as the cathode and anode, and immerse the two electrodes (with a spacing of 1.5cm) in 100mL of electrolyte solution to form a single-chamber electrolytic cell. Then add a 2mM sodium sulfite solution that has been pre-adjusted to a pH of 7 to the reactor, and the total volume of the system is 100ml. Direct current is then applied to start the reaction. Use a DC regulated power supply to set a constant current of 60mA (i.e., a current density of 37.5A / m 2 ) and the reaction temperature was adjusted to 25°C using a water bath. During the reaction, water samples were taken at different reaction time points to determine the residual concentration of chlorite, the concentration of chloride ions generated by reduction, and the residual concentration of carbamazepine. Chlorite and chloride ion reduction curves, as well as carbamazepine degradation curves, were plotted under different reaction time conditions.

[0057] As shown in Figure 4, as the reaction proceeds, the reducing power of the electroactivated sulfite system gradually weakens, while its oxidizing power gradually strengthens. After 5 minutes of reaction, all chlorite is reduced to chloride ions, meeting the limit requirement of 0.7 mg / L in the "Sanitary Standard for Drinking Water (GB5749-2022)". After 30 minutes of reaction, the carbamazepine removal rate reaches 63%. When treating slightly polluted source water or chlorine dioxide disinfection effluent, no additional electrolyte is required. Using sulfite and chlorite as electrolytes, the disinfection byproduct chlorite and new chlorine dioxide-resistant organic pollutants can be simultaneously removed. At this point, all sulfite is oxidized to sulfate, and the sulfate ion concentration in the system is approximately 250 mg / L, meeting the limit requirement of 250 mg / L in the "Sanitary Standard for Drinking Water (GB5749-2022)".

Claims

1. A method for removing water pollutants by electro-activating sulfite, characterized in that: include: A sulfite solution is added to the water containing pollutants, and then direct current is passed through and stirred continuously to remove organic pollution and / or inorganic pollutants in the water.

2. The method for removing water pollutants by electro-activating sulfite according to claim 1, characterized in that: When the DC current is 100-300 mA and the concentration of the sulfite solution is 2-4 mM, the rate of removing organic pollutants in the water is 0.031-0.17 min -1 .

3. The method for removing water pollutants by electro-activating sulfite according to claim 2, characterized in that: Before adding the sulfite solution to the pollutant-containing water body, the pH of the pollutant-containing water body is adjusted to be above 7.

4. The method for removing water pollutants by electro-activating sulfite according to claim 1, characterized in that: When the DC current is 20-40 mA and the concentration of the sulfite solution is 2-6 mM, the rate of removing inorganic pollutants in the water is 0.023-0.12 min -1 .

5. The method for removing water pollutants by electro-activating sulfite according to claim 4, characterized in that: Before adding the sulfite solution to the pollutant-containing water body, the pH of the pollutant-containing water body is adjusted to below 6.

5.

6. The method for removing water pollutants by electro-activating sulfite according to claim 1, characterized in that: When the DC current is 60-100 mA and the concentration of the sulfite solution is 2-4 mM, the rate of removing organic pollutants in the water is 0.015-0.028 min -1 The rate of removing inorganic pollutants from water is 0.019-0.077min -1 .

7. The method for removing water pollutants by electro-activating sulfite according to claim 6, characterized in that: Before adding the sulfite solution to the pollutant-containing water body, the pH of the pollutant-containing water body is adjusted to 6-9.

8. The method for removing water pollutants by electro-activating sulfite according to claim 1, characterized in that: The stirring speed is 400-800 rpm.

9. The method for removing water pollutants by electro-activating sulfite according to claim 1, characterized in that: The organic pollutants include any one or more of antibiotics, pesticides and endocrine disruptors, and the inorganic pollutants include any one or more of chlorite, chlorate, bromate and dichromate.

10. The method for removing water pollutants by electro-activating sulfite according to claim 1, characterized in that: An electrochemical reactor is formed by inserting positive and negative electrodes into a water body containing pollutants so as to pass direct current into the water body containing pollutants. Both the positive and negative electrodes are titanium-based ruthenium-iridium mixed metal oxide electrodes.

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