Method for the electrochemical cathodic and anodic synergistic treatment of ship ballast water

Abstract

The present application belongs to the technical field of electrochemical treatment of ballast water, and provides a method for treating ship ballast water by using electrochemical cathode and anode in cooperation, wherein the anode and the cathode are placed in a static electrolytic cell containing ship ballast water or a flow electrolytic cell containing ship ballast water, oxygen or air diffuses to the cathode to produce active species through a reduction reaction; the anode electro-oxidizes seawater or chloride ions to produce active species, and the cathode electro-reduces oxygen to produce active species. The method for treating ship ballast water by using electrochemical cathode and anode in cooperation is a green and efficient technology, wherein the anode electro-oxidizes seawater or chloride ions to produce active species such as chlorine free radicals, hydroxyl free radicals and ozone, and the cathode electro-reduces oxygen to produce active species such as hydroxyl free radicals, singlet oxygen and hydrogen peroxide, which have strong oxidation ability and are environmentally friendly, and have good inactivation effect on bacteria, viruses, plankton, algae and other organisms in the ballast water without generating by-products.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrochemical treatment of ballast water, and in particular to a method for treating ship ballast water by using electrochemical cathode and anode in cooperation. BACKGROUND

[0002] Ship ballast water contains a large amount of aquatic organisms such as bacteria, viruses, plankton and algae. Discharging untreated ballast water to a different place during shipping can lead to the invasion of foreign organisms, which seriously threatens the local marine ecological environment and human health. The International Convention for the Control and Management of Ships' Ballast Water and Sediments (IM0) stipulates that the discharged ballast water must meet the specific biological survival quantity limit. Therefore, it is very important to study efficient ballast water treatment technology to meet the convention standards and protect the marine ecological environment. At present, the main treatment technologies for ship ballast water include chlorine treatment, ultraviolet disinfection and electrolytic oxidation method. Chlorine treatment technology has the risk of producing carcinogens such as trihalomethane, and studies have shown that chlorine treatment technology cannot significantly reduce the colonization pressure of plankton; the treatment performance of ultraviolet disinfection technology is easily affected by water turbidity, thereby reducing the efficiency of biological inactivation, which is not suitable for scenarios with large amount of ballast water. Electrolytic oxidation method produces a large amount of chlorine-containing substances such as chlorine and hypochlorous acid during the treatment process, which corrodes the ballast tank and pipeline, and the maintenance cost is high. Therefore, it is urgent to develop green and efficient ballast water treatment technology with wide application range.

[0003] Electrochemical technology has become an important development direction for ballast water treatment technology due to its simple device, small occupied space, easy operation and low energy consumption. However, the current electrolytic oxidation method mainly uses anode oxidation to produce chlorine-containing substances, which is not easy to control and maintain, and the cathode does not play a role, reducing the energy utilization efficiency of the electrolytic cell. Previous studies have found that electrodes doped with tin oxide, titanium suboxide, ruthenium iridium titanium and diamond have high oxygen evolution overpotential and good electro-oxidation activity (Environ. Sci. Technol. 2019, 53:5195-5201; Chin Chem Lett 2024, 35:108704). Electro-oxidation of chlorine-containing ion solution can produce chlorine radicals, hydroxyl radicals, etc., while carbon nanotube, activated carbon, carbon black or porous carbon-based carbon materials or composite cathodes with transition metals have high activity in electro-reducing oxygen (Angew Chem Int Edit 2015, 54:6837-6841), which can produce hydroxyl radicals, singlet oxygen and hydrogen peroxide. The use of one or more active species produced by the anode and cathode and the direct electro-oxidation and reduction of the electrode is expected to significantly improve the treatment effect and improve the energy utilization efficiency. SUMMARY

[0004] The present application aims to provide a method for treating ship ballast water by electrochemical cathode and anode cooperation in order to overcome the shortcomings of the prior art.

[0005] In order to achieve the above-mentioned application purposes, the present application provides the following technical solutions:

[0006] The present application provides a method for treating ship ballast water by electrochemical cathode and anode cooperation, which places an anode and a cathode in a static electrolytic cell containing ship ballast water or a flow electrolytic cell containing ship ballast water, diffuses oxygen or air to the cathode through solution aeration or gas diffusion electrode to generate an oxygen reduction reaction;

[0007] The electrolytic cell applies a constant voltage, a constant current or a pulse current;

[0008] The anode electro-oxidizes seawater or chloride ions to generate active species, the cathode electro-reduces oxygen to generate active species, and the active species generated by the cathode and the anode cooperate to inactivate the organisms in the ballast water.

[0009] As a preferred, the active species generated by the anode electro-oxidizing seawater or chloride ions include one or several of hydroxyl radicals, chlorine radicals and ozone; the active species generated by the cathode electro-reducing oxygen include one or several of hydroxyl radicals, singlet oxygen, hydrogen peroxide and superoxide hydrogen radicals.

[0010] As a preferred, the active species generated by the cathode electro-reducing oxygen oxidize at the interface of the cathode and the anode or diffuse into the bulk solution to oxidize, and the oxidation inactivates the organisms in the ballast water.

[0011] As a preferred, the anode is a material with high oxygen evolution overpotential; the cathode is a carbon material, a transition metal single-atom catalyst or a composite material of a transition metal and a carbon material, the carbon material is an undoped carbon material or a heteroatom-doped carbon material, and the carbon material includes carbon nanotubes, activated carbon, carbon black or porous carbon.

[0012] As a preferred, the cathode is a boron-oxygen co-doped carbon nanotube electrode or an oxidized carbon nanotube electrode; the anode is a ruthenium-iridium-titanium electrode, a doped tin oxide electrode, a boron-nitrogen-doped diamond electrode or a sub-oxidized titanium electrode.

[0013] As a preferred, the preparation method of the boron-oxygen co-doped carbon nanotube electrode includes the following steps:

[0014] 1) After acidizing treatment of the carbon nanotubes in mixed acid and water washing to neutral, acid-treated carbon nanotubes are obtained;

[0015] 2) The acid-treated carbon nanotubes and boric acid are calcined under a protective atmosphere to obtain boron-oxygen co-doped carbon nanotube powder;

[0016] 3) ultrasonic dispersion of the mixture of the boron-oxygen co-doped carbon nanotube powder, the Nafion film solution and water, and coating the dispersed catalyst on a hydrophobic carbon cloth to obtain a boron-oxygen co-doped carbon nanotube cathode.

[0017] Preferably, the mixed acid in step 1) comprises concentrated nitric acid and concentrated sulfuric acid, the volume ratio of the concentrated nitric acid and the concentrated sulfuric acid is 1:2-4, the acidification treatment temperature is 60-120℃, and the acidification treatment time is 0.5-6h;

[0018] The mass ratio of the acid-treated carbon nanotube and boric acid in step 2) is 1:2-13, the calcination temperature is 600-1000℃, and the calcination time is 0.5-5h;

[0019] The mass-volume ratio of the boron-oxygen co-doped carbon nanotube powder, the Nafion film solution and water in step 3) is 10-30mg:180-220μL:1500-1700μL, and the ultrasonic dispersion time is 10-30min.

[0020] The beneficial effects of the present application include the following points:

[0021] 1) The electrochemical cathode and anode synergistic treatment of ballast water is a green and efficient technology, the present application generates active species such as chlorine free radicals, hydroxyl radicals and ozone by anodic electro-oxidation of seawater or chloride ions, and generates active species such as hydroxyl radicals, singlet oxygen and hydrogen peroxide by cathodic electro-reduction of oxygen, which has strong oxidation ability, is environmentally friendly, and has good inactivation effect on bacteria, viruses, plankton and algae in ballast water without by-products. In addition, the direct electro-oxidation and reduction of the anode and the cathode is also conducive to biological inactivation; one or more active species synergistically achieve energy saving and efficiency improvement, overcoming the defects of low biological inactivation efficiency, pollution and corrosion of existing ballast water treatment technology.

[0022] 2) The present application uses chlorine free radicals, hydroxyl radicals and singlet oxygen as the main active species, and uses chloride ions and oxygen in the ballast water as reactants, without the need for additional reactants, and the method is simple, clean, low in cost and fast in processing speed, and is a sustainable technology for pollution reduction and carbon reduction; the electrochemical cathode and anode synergistic technology can significantly improve the treatment performance and energy utilization efficiency of the electrochemical system; the electrochemical system is easy to modularize, and can be flexibly adjusted based on electrochemical parameters, types and yields of active species for different working conditions (processing capacity, ship structure, etc.), to realize efficient ballast water treatment, and has a wide application prospect.

[0023] 3) The application is based on the chemical composition and structural design of the anode and cathode to inhibit the generation of chlorine and the accumulation of hypochlorous acid, improve the yield and utilization rate of other active species, and further improve the performance of ballast water treatment. The anode of the application can use electrodes such as doped tin oxide, titanium suboxide, ruthenium iridium titanium, and doped diamond with high oxygen evolution overpotential, and the cathode can use electrodes such as carbon materials, transition metal single-atom catalysts, and composite materials of transition metals and carbon materials with high oxygen reduction activity. The application can achieve efficient sterilization and algae removal of ballast water in a short time, reduce the risk of invasive species, has the advantages of good stability of anode and cathode, simple method, environmental friendliness, low cost, and is easy to realize large-scale application, which has important significance for protecting the marine ecological environment and promoting the sustainable development of global shipping industry. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 The diatom removal rates of the ballast water treated by the electrochemical system of Example 1 under different cathode potentials and different hydraulic retention times, wherein a is the cathode potential -0.8V, and b is the cathode potential -0.4V;

[0025] Figure 2 The diatom removal rates of the ballast water treated by the anode and cathode synergistic system of Example 2 and the single anode or single cathode of Comparative Example 1;

[0026] Figure 3 The diatom removal rates of the ballast water treated by the anode and cathode synergistic system of Example 2 and the single anode or single cathode of Comparative Example 1. DETAILED DESCRIPTION

[0027] The application provides a method for treating ballast water of a ship by using an electrochemical cathode and anode in cooperation, wherein the anode and the cathode are placed in a static electrolytic cell containing the ballast water of the ship or a flow electrolytic cell containing the ballast water of the ship, oxygen or air is diffused to the cathode to occur an oxygen reduction reaction through solution aeration or a gas diffusion electrode;

[0028] The electrolytic cell applies a constant voltage, a constant current or a pulse current;

[0029] The anode electro-oxidizes seawater or chloride ions to produce active species, the cathode electro-reduces oxygen to produce active species, and the active species produced by the cathode and the anode synergistically inactivate the organisms in the ballast water.

[0030] In the application, the active species produced by the anode electro-oxidizing seawater or chloride ions preferably include one or more of hydroxyl radicals, chlorine radicals and ozone; and the active species produced by the cathode electro-reducing oxygen preferably include one or more of hydroxyl radicals, singlet oxygen, hydrogen peroxide and superoxide hydrogen radicals.

[0031] In the present application, the active species generated by the cathodic reduction of oxygen is oxidized at the interface of the anode and the cathode or diffuses into the bulk solution to be oxidized, and the oxidation reaction inactivates the organisms in the ballast water.

[0032] In the present application, one or more of the active species generated by the anodic oxidation of seawater or chloride ions and the active species generated by the cathodic reduction of oxygen are coupled with direct electro-oxidation and reduction, thereby inactivating the organisms in the ballast water.

[0033] In the present application, the anode is preferably a material with a high oxygen evolution overpotential; the cathode is preferably a carbon material, a transition metal single-atom catalyst, or a composite material of a transition metal and a carbon material, and the carbon material is preferably an undoped carbon material or a heteroatom-doped carbon material, and the carbon material preferably comprises carbon nanotubes, activated carbon, carbon black, or porous carbon.

[0034] In the present application, the cathode is preferably a boron-oxygen co-doped carbon nanotube electrode or an oxidized carbon nanotube electrode; and the anode is preferably a ruthenium-iridium-titanium electrode, a doped tin oxide electrode, a boron-nitrogen-doped diamond electrode, or a sub-oxidized titanium electrode.

[0035] In the present application, the preparation method of the boron-oxygen co-doped carbon nanotube electrode comprises the following steps:

[0036] 1) Acidifying carbon nanotubes in a mixed acid and washing to neutral to obtain acid-treated carbon nanotubes;

[0037] 2) Calcining the acid-treated carbon nanotubes and boric acid under a protective atmosphere to obtain boron-oxygen co-doped carbon nanotube powder;

[0038] 3) Mixing the boron-oxygen co-doped carbon nanotube powder, a Nafion film solution, and water, and then ultrasonic dispersing, and coating the dispersed catalyst on a hydrophobic carbon cloth to obtain a boron-oxygen co-doped carbon nanotube cathode.

[0039] In the present application, the mixed acid in step 1) preferably comprises concentrated nitric acid and concentrated sulfuric acid, and the volume ratio of the concentrated nitric acid to the concentrated sulfuric acid is preferably 1:2-4, further preferably 1:2.5-3.5, and more preferably 1:3; the acidification temperature is preferably 60-120℃, further preferably 70-100℃, and more preferably 80-90℃; and the acidification time is preferably 0.5-6h, further preferably 1-4h, and more preferably 2-3h.

[0040] In step 2), the mass ratio of the acid-treated carbon nanotubes to boric acid is preferably 1:2-13, further preferably 1:4-12, and more preferably 1:8-10; the calcination temperature is preferably 600-1000℃, further preferably 650-900℃, and more preferably 700-800℃; and the calcination time is preferably 0.5-5h, further preferably 1-4h, and more preferably 2-3h.

[0041] The mass-volume ratio of the boron-oxygen co-doped carbon nanotube powder, the Nafion film solution and water in step 3) is preferably 10-30 mg: 180-220 μL: 1500-1700 μL, further preferably 15-25 mg: 190-210 μL: 1550-1650 μL, more preferably 20 mg: 200 μL: 1600 μL; and the ultrasonic dispersion time is preferably 10-30 min, further preferably 15-25 min, more preferably 20 min.

[0042] In the present application, the coating amount in step 3) is preferably 0.5-3.0 mg / cm 2 , further preferably 1-2.5 mg / cm 2 , more preferably 1.5-2.0 mg / cm 2 .

[0043] In the present application, the boron-nitrogen doped diamond electrode is prepared by plasma chemical vapor deposition in a mixed gas using a titanium sheet as a substrate.

[0044] The mixed gas preferably comprises methane, hydrogen, nitrogen and borane.

[0045] In the mixed gas of the present application, the volume fraction of methane is preferably 1-3%, further preferably 2.5%, the volume fraction of hydrogen is preferably 83-87%, further preferably 84-86%, more preferably 85%, the volume fraction of nitrogen is preferably 2-3%, further preferably 2.5%, the volume fraction of borane is preferably 9-11%, further preferably 9.5-10.5%, more preferably 10%; the temperature of the plasma chemical vapor deposition is preferably 580-620°C, further preferably 590-610°C, more preferably 600°C, the pressure is preferably 580-620 Pa, further preferably 590-610 Pa, more preferably 600 Pa, and the time is preferably 9-11 h, further preferably 9.5-10.5 h, more preferably 10 h.

[0046] The technical solutions provided by the present application will be described in detail below in conjunction with the examples, but they should not be understood as limiting the scope of protection of the present application.

[0047] Example 1

[0048] The boron-oxygen co-doped carbon nanotube (B, O-CNT) electrode is used as a cathode, and a commercially available ruthenium iridium titanium electrode is used as an anode, the cathode and the anode are arranged in a flow state electrolytic cell containing ship ballast water, seawater containing algae enters from the lower part of the anode chamber, and seawater exits from the upper part of the cathode chamber, wires are used to connect the two electrodes and apply a constant voltage, a continuous flow water inlet mode is adopted, and aeration is carried out at the cathode to supplement the dissolved oxygen in the water to facilitate the use of the cathode, and active species (hydroxyl radicals, singlet oxygen, hydrogen peroxide and superoxide hydrogen radicals) are generated at the anode-cathode interface to oxidize the active species (hydroxyl radicals, chlorine radicals and ozone) to inactivate the organisms in the ballast water.

[0049] The preparation method of the B, O-CNT electrode is as follows: carbon nanotubes are immersed in mixed acid (the volume ratio of concentrated nitric acid and concentrated sulfuric acid is 1:3), and acidification treatment is carried out at 80℃ in a water bath for 2h, and after water washing to neutral, the acid-treated carbon nanotubes are uniformly mixed with boric acid at a mass ratio of 1:10, and calcination is carried out at 700℃ for 1h under the protection of argon atmosphere, to obtain B, O-CNT powder. 20mg of B, O-CNT powder is mixed with 200μL of Nafion film solution, 1600μL of high-purity water, and then ultrasonic dispersion (power is 800W) treatment is carried out for 20min, and the dispersed catalyst is coated on a hydrophobic carbon cloth (the catalyst loading is 2.0mg / cm 2 ) as a boron-oxygen co-doped carbon nanotube cathode.

[0050] In the process of treating diatoms in seawater, the concentration of diatoms in the inlet water is 5.0×10 6 / mL, the hydraulic retention time is controlled to be 1.5min and 2min respectively, the cathode potential is-0.4V and-0.8V (vs Ag / AgCl) respectively, and the diatom removal experiment is carried out, and the water is taken out at 3min, 5min, 10min, 20min and 30min respectively for detection.

[0051] The diatom removal rates of the ballast water treated by the electrochemical system of example 1 under different cathode potentials and different hydraulic retention times are as shown in Figure 1 , wherein a is the cathode potential-0.8V, and b is the cathode potential-0.4V. Figure 1 It can be known from the above table that the electrochemical system of the present application has high diatom removal performance, and when the cathode potential is-0.4V and the hydraulic retention time is 1.5min and 2min, the diatom removal rate is maintained at 92.1-94.1% under continuous flow conditions; when the cathode bias is increased to-0.8V, the diatom removal rate is increased to 99.5%.

[0052] Example 2

[0053] Carbon oxide nanotube (OCNT) electrodes are used as cathodes and boron, n-doped diamond (BND) electrodes are used as anodes. The cathodes and anodes are placed in a dynamic electrolysis cell containing ship ballast water. Seawater containing algae enters from the lower part of the anode chamber and exits from the upper part of the cathode chamber. The two electrodes are connected by wires and pulsed currents are applied (alternating between -0.8V, 1.5min and 0V, 0.5min). A continuous flow of water is used. Aeration is performed at the cathode to supplement dissolved oxygen in the water for cathode utilization. The generated active species (hydroxyl radicals, singlet oxygen, hydrogen peroxide, and superoxide radicals) undergo oxidation reactions at the anode-cathode interface, which inactivates the organisms in the ballast water. The anode electro-oxidizes seawater or chloride ions to generate active species (hydroxyl radicals, chloride radicals, and ozone).

[0054] The BND electrode is prepared by using a Ti sheet as a substrate and performing plasma chemical vapor deposition in a mixed gas with volume fractions of 2.5% methane, 85% hydrogen, 2.5% nitrogen and 10% borane. The substrate temperature is 600℃, the plasma chemical vapor deposition pressure is 600Pa, and the deposition time is 10h.

[0055] Diatoms (5.0 × 10⁻⁶) in seawater were treated with a cathode bias of -0.8 V and a hydraulic residence time of 2 min. 6 (crystals / mL) and golden algae (4.0 × 10⁻⁶) 6 The treatment time was 1 hour (number of cells / mL).

[0056] Comparative Example 1

[0057] For separate cathode or anode treatment, the carbon oxide nanotube (OCNT) electrode is used as the cathode and the BND electrode is used as the anode. The cathode chamber and the anode chamber are separated by a proton exchange membrane, and water enters and exits separately at the cathode and anode. Other conditions are the same as in Example 2.

[0058] The removal rates of diatoms by the anode-cathode synergistic system in Example 2 and by the single cathode or single anode in Comparative Example 1 are as follows: Figure 2 As shown, the removal rates of golden algae by the synergistic cathode and cathode system of Example 2 and the single cathode or single anode of Comparative Example 1 are as follows: Figure 3 As shown. By Figure 2 and Figure 3 It can be seen that within a 1-hour operating cycle, the removal rate of diatoms and golden algae in the effluent of the anode-cathode synergistic system remains at around 100%. The removal performance of diatoms and golden algae by anode alone is better than that of cathode alone. For golden algae, the removal rate of the anode-cathode synergistic system is significantly higher than that of anode alone or cathode alone. Compared with cathode or anode treatment alone, the anode-cathode synergistic technology shows higher removal efficiency and longer stabilization time for diatoms and golden algae, proving that the anode-cathode synergistic technology has a more efficient biological inactivation function for ballast water.

[0059] Example 3

[0060] The cathode was undoped activated carbon material, the anode was titanium suboxide electrode, and other conditions were the same as in Example 1.

[0061] The above only describes the preferred embodiments of the present application, and it should be noted that for those skilled in the art, several improvements and refinements can be made without departing from the principles of the present application, and these improvements and refinements should also be considered within the scope of protection of the present application.

Claims

1. A method of electrochemically cathodically and anodically treating ship ballast water, characterized in that, The anode and the cathode are placed in a static electrolytic cell containing ship ballast water or a flow electrolytic cell containing ship ballast water, and oxygen or air is diffused to the cathode through solution aeration or gas diffusion electrode to cause oxygen reduction reaction; The electrolytic cell applies constant voltage, constant current or pulse electricity; The anode electro-oxidizes seawater or chloride ions to produce active species, and the cathode electro-reduces oxygen to produce active species, and the active species produced by the cathode and the anode synergistically inactivate the organisms in the ballast water; The cathode is a boron-oxygen co-doped carbon nanotube electrode, and the anode is a ruthenium-iridium-titanium electrode, a doped tin oxide electrode, a boron-nitrogen-doped diamond electrode or a sub-titanium oxide electrode; The preparation method of the boron-oxygen co-doped carbon nanotube electrode comprises the following steps: 1) The carbon nanotubes are placed in mixed acid for acidification treatment, then washed to neutral, and acid-treated carbon nanotubes are obtained; 2) The acid-treated carbon nanotubes and boric acid are calcined under a protective atmosphere to obtain boron-oxygen co-doped carbon nanotube powder; 3) The boron-oxygen co-doped carbon nanotube powder, Nafion film solution and water are mixed and ultrasonically dispersed, and the dispersed catalyst is coated on a hydrophobic carbon cloth to obtain a boron-oxygen co-doped carbon nanotube cathode; In step 1), the mixed acid comprises concentrated nitric acid and concentrated sulfuric acid, the volume ratio of concentrated nitric acid to concentrated sulfuric acid is 1:2-4, the acidification treatment temperature is 60-120℃, and the acidification treatment time is 0.5-6h; In step 2), the mass ratio of the acid-treated carbon nanotubes to boric acid is 1:2-13, the calcination temperature is 600-1000℃, and the calcination time is 0.5-5h; In step 3), the mass-volume ratio of the boron-oxygen co-doped carbon nanotube powder, Nafion film solution and water is 10-30mg:180-220μL:1500-1700μL, and the ultrasonic dispersion time is 10-30min. The active species produced by the anode electro-oxidizing seawater or chloride ions include one or more of hydroxyl radicals, chlorine radicals and ozone; and the active species produced by the cathode electro-reducing oxygen include one or more of hydroxyl radicals, singlet oxygen, hydrogen peroxide and superoxide hydrogen radicals.

2. The method of claim 1, wherein, The active species produced by the cathode electro-reducing oxygen undergo oxidation reaction at the anode-cathode interface or diffuse into the bulk solution to undergo oxidation reaction, and the oxidation reaction inactivates the organisms in the ballast water.

3. The method according to claim 1 or 2, characterized in that, ​

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