Method for cooperatively treating ship ballast water through electrochemical cathode and anode

Abstract

The invention belongs to the technical field of electrochemical treatment of ballast water, and provides a method for cooperatively treating ship ballast water by using an electrochemical cathode and an electrochemical anode, which comprises the following steps of: placing the anode and the cathode in a static electrolytic tank containing the ship ballast water or a flowing electrolytic tank containing the ship ballast water; oxygen or air diffuses to the cathode for reduction reaction to generate active species; the anode electrooxidizes seawater or chloride ions to generate active species, and the cathode electroreduces oxygen to generate active species. The method for cooperatively treating ballast water through the electrochemical cathode and the anode is a green and efficient technology, seawater or chloride ions are subjected to electrooxidation through the anode to generate active species such as chlorine free radicals, hydroxyl free radicals and ozone, oxygen is subjected to electroreduction through the cathode to generate active species such as hydroxyl free radicals, singlet oxygen and hydrogen peroxide, and therefore the ballast water is treated through the cathode and the anode. The active species are high in oxidation capacity, environment-friendly, good in inactivation effect on bacteria, viruses, plankton, algae and other organisms in the ballast water and free of by-products.

Description

Technical Field

[0001] The invention relates to the technical field of electrochemical treatment of ballast water, and in particular to a method for co-treatment of ship ballast water by electrochemical cathode and anode. Background Art

[0002] Ship ballast water contains a large number of aquatic organisms such as bacteria, viruses, plankton, and algae. The discharge of untreated ballast water in other places during shipping will lead to the invasion of foreign organisms, which seriously threatens the local marine ecological environment and human health. The global annual ballast water discharge is as high as about 10 billion tons. The International Convention for the Control and Management of Ships' Ballast Water and Sediments promulgated by the International Maritime Organization (IMO) clearly stipulates that the discharged ballast water must meet specific biological survival limits. Therefore, it is very important to study efficient ballast water treatment technology to meet the standards of the convention and protect the marine ecological environment. At present, the treatment technologies for ship ballast water mainly include chlorine treatment, ultraviolet disinfection, and electrolytic oxidation. Chlorine treatment technology has the risk of producing carcinogens such as trihalomethanes, and studies have shown that chlorine treatment technology cannot significantly reduce the colonization pressure of zooplankton; while the treatment performance of ultraviolet disinfection technology is easily affected by water turbidity, thereby reducing the efficiency of biological inactivation, and is not applicable to scenarios with large ballast water treatment volumes. Electrolytic oxidation will produce a large amount of chlorine-containing substances such as chlorine gas and hypochlorous acid during the treatment process, which will corrode ballast tanks and pipelines and have high maintenance costs. Therefore, there is an urgent need to develop green, efficient and widely applicable ballast water treatment technology.

[0003] Electrochemical technology has become an important development direction of ballast water treatment technology due to its simple device, small footprint, easy operation and low energy consumption. However, the current electrolytic oxidation method mainly uses anodic oxidation to produce chlorine-containing substances, which is difficult 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 monoxide, 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 chloride-containing solutions can produce chlorine radicals, hydroxyl radicals, etc., and carbon materials such as carbon nanotubes, activated carbon, carbon black or porous carbon or composite cathodes with transition metals have high oxygen reduction activity (Angew Chem Int Edit 2015, 54: 6837-6841), which can produce hydroxyl radicals, singlet oxygen, hydrogen peroxide, etc. The use of one or more active species produced at the anode and cathode and the direct electrical redox effect of the electrodes is expected to significantly improve the treatment effect and increase energy utilization efficiency. Summary of the invention

[0004] The purpose of the present invention is to provide a method for cooperating electrochemical cathode and anode to treat ship ballast water in order to overcome the shortcomings of the prior art.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a method for co-processing ship ballast water by using an electrochemical cathode and an anode. The anode and the cathode are placed in a static electrolytic cell containing ship ballast water or a flowing electrolytic cell containing ship ballast water. Oxygen or air diffuses to the cathode through a solution aeration or a gas diffusion electrode to cause an oxygen reduction reaction.

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

[0008] The anode electro-oxidizes seawater or chloride ions to produce active species, and the cathode electro-reduces oxygen to produce active species. The active species produced at the cathode and anode act synergistically to inactivate organisms in the ballast water.

[0009] Preferably, the active species produced by the electro-oxidation of seawater or chloride ions at the anode include one or more of hydroxyl radicals, chlorine radicals and ozone; the active species produced by the electro-reduction of oxygen at the cathode include one or more of hydroxyl radicals, singlet oxygen, hydrogen peroxide and superoxide radicals.

[0010] Preferably, the active species generated by the cathode electroreduction of oxygen undergo an oxidation reaction at the anode-cathode interface or diffuse into the bulk solution to undergo an oxidation reaction, and the oxidation reaction inactivates the organisms in the ballast water.

[0011] Preferably, the anode is a material with a 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 comprises carbon nanotubes, activated carbon, carbon black or porous carbon.

[0012] Preferably, 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-titanium oxide electrode.

[0013] Preferably, the method for preparing the boron-oxygen co-doped carbon nanotube electrode comprises the following steps:

[0014] 1) placing carbon nanotubes in mixed acid for acidification treatment and then washing with water until neutrality to obtain acid-treated carbon nanotubes;

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

[0016] 3) Boron and oxygen co-doped carbon nanotube powder, Nafion membrane solution and water are mixed and then ultrasonically dispersed, and the dispersed catalyst is coated on a hydrophobic carbon cloth to obtain a boron and 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 concentrated nitric acid to concentrated sulfuric acid is 1:2-4, the temperature of the acidification treatment is 60-120° C., and the time of the acidification treatment is 0.5-6 h;

[0018] Step 2) the mass ratio of the acid-treated carbon nanotubes to boric acid is 1:2-13; the calcination temperature is 600-1000°C, and the calcination time is 0.5-5h;

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

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

[0021] 1) The electrochemical cathode and anode synergistic treatment of ballast water is a green and efficient technology. The present invention generates active species such as chlorine free radicals, hydroxyl free radicals, and ozone by electro-oxidizing seawater or chloride ions at the anode, and generates active species such as hydroxyl free radicals, singlet oxygen, and hydrogen peroxide by electro-reducing oxygen at the cathode. These active species have strong oxidizing ability and are environmentally friendly. They have good inactivation effects on bacteria, viruses, plankton, algae and other organisms in ballast water, and no by-products are produced. In addition, the direct electrical oxidation-reduction effect of the anode and cathode is also conducive to biological inactivation; one or more active species work synergistically to achieve energy saving and efficiency improvement, overcoming the defects of low biological inactivation efficiency, pollution and corrosion in existing ballast water treatment technologies.

[0022] 2) The present invention uses chlorine radicals, hydroxyl radicals, singlet oxygen, etc. as main active species, and chloride ions and oxygen in ballast water as reactants. No additional reactants need to be added. The method is simple, clean, low-cost, and has a fast processing speed. It is a sustainable technology for reducing pollution and carbon emissions. The electrochemical cathode and anode synergistic technology can achieve a significant improvement in 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 of active species, and yields for different working conditions (processing volume, ship structure, etc.), so as to achieve efficient ballast water treatment, and has broad application prospects.

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

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

[0025] Figure 2 The removal rate of diatoms by the cathode-anode cooperative system of Example 2 and the cathode alone or the anode alone of Comparative Example 1;

[0026] Figure 3 The removal rates of golden algae by the cathodic cooperative system of Example 2 and the single cathode or single anode of Comparative Example 1. DETAILED DESCRIPTION

[0027] The present invention provides a method for co-processing ship ballast water by using an electrochemical cathode and an anode. The anode and the cathode are placed in a static electrolytic cell containing ship ballast water or a flowing electrolytic cell containing ship ballast water. Oxygen or air diffuses to the cathode through a solution aeration or a gas diffusion electrode to cause an oxygen reduction reaction.

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

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

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

[0031] In the present invention, active species generated by cathode electroreduction of oxygen undergo oxidation reaction at the anode-cathode interface or diffuse into the bulk solution to undergo oxidation reaction, and the oxidation reaction inactivates organisms in the ballast water.

[0032] In the present invention, one or more of the active species generated by the electro-oxidation of seawater or chloride ions at the anode and the active species generated by the electro-reduction of oxygen at the cathode are coupled with direct electro-oxidation-reduction to inactivate the organisms in the ballast water.

[0033] In the present invention, 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, 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 invention, the cathode is preferably a boron-oxygen co-doped carbon nanotube electrode or an oxidized carbon nanotube electrode; the anode is preferably a ruthenium-iridium-titanium electrode, a doped tin oxide electrode, a boron-nitrogen doped diamond electrode or a sub-titanium oxide electrode.

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

[0036] 1) placing carbon nanotubes in mixed acid for acidification treatment and then washing with water until neutrality 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) Boron and oxygen co-doped carbon nanotube powder, Nafion membrane solution and water are mixed and then ultrasonically dispersed, and the dispersed catalyst is coated on a hydrophobic carbon cloth to obtain a boron and oxygen co-doped carbon nanotube cathode.

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

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

[0041] Step 3) The mass volume ratio of the boron-oxygen co-doped carbon nanotube powder, Nafion membrane solution and water 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; the ultrasonic dispersion time is preferably 10-30 min, further preferably 15-25 min, more preferably 20 min.

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

[0043] In the present invention, the method for preparing the boron-nitrogen doped diamond electrode is as follows: using a titanium sheet as a substrate, performing plasma chemical vapor deposition in a mixed gas to obtain a boron-nitrogen doped diamond electrode;

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

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

[0046] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0047] Example 1

[0048] A boron-oxygen co-doped carbon nanotube (B,O-CNT) electrode is used as the cathode, and a commercially available ruthenium-iridium-titanium electrode is used as the anode. The cathode and the anode are placed in a flow 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. A wire is used to connect the two electrodes and a constant voltage is applied. A continuous flow water inlet method is adopted. Aeration is performed at the cathode to supplement the dissolved oxygen in the water for cathode utilization. The generated active species (hydroxyl radicals, singlet oxygen, hydrogen peroxide and superoxide radicals) undergo oxidation reaction at the anode-cathode interface, and the oxidation reaction inactivates the organisms in the ballast water. The anode electro-oxidizes seawater or chloride ions to produce active species (hydroxyl radicals, chlorine radicals and ozone).

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

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

[0051] The diatom removal rate of the electrochemical system for treating ballast water in Example 1 at different cathode potentials and different hydraulic retention times is as follows: Figure 1 As shown, a is the cathode potential -0.8V, b is the cathode potential -0.4V. Figure 1 It can be seen that the electrochemical system of the present invention exhibits efficient diatom removal performance. At -0.4 V and a hydraulic retention time of 1.5 min and 2 min, the diatom removal rate under continuous flow conditions is maintained at 92.1-94.1%; when the cathode bias voltage is increased to -0.8 V, the diatom removal rate rises to 99.5%.

[0052] Example 2

[0053] An oxidized carbon nanotube (OCNT) electrode is used as the cathode and a B,N doped diamond (BND) electrode is used as the anode. The cathode and the anode are placed in a flow 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. A wire is used to connect the two electrodes and pulse electricity is applied (alternating between -0.8V, 1.5min and 0V, 0.5min). A continuous flow water inlet method is adopted, and aeration is performed at the cathode to supplement the dissolved oxygen in the water for cathode utilization. The generated active species (hydroxyl radicals, singlet oxygen, hydrogen peroxide and superoxide radicals) undergo oxidation reaction at the anode-cathode interface, and the oxidation reaction inactivates the organisms in the ballast water; the anode electrooxidizes seawater or chloride ions to produce active species (hydroxyl radicals, chlorine radicals and ozone).

[0054] The preparation method of BND electrode is as follows: using Ti sheet as substrate, plasma chemical vapor deposition is carried out in a mixed gas of 2.5% methane, 85% hydrogen, 2.5% nitrogen and 10% borane by volume, the substrate temperature is 600°C, the pressure of plasma chemical vapor deposition is 600Pa, and the deposition time is 10h.

[0055] When the cathode bias voltage was controlled at -0.8 V and the hydraulic retention time was 2 min, the diatoms (5.0×10 6 / mL) and golden algae (4.0×10 6 / mL), and the treatment time was 1h.

[0056] Comparative Example 1

[0057] In single cathode or anode treatment, the oxidized carbon nanotube (OCNT) electrode is the cathode, the BND electrode is the anode, the cathode chamber and the anode chamber are separated by a proton exchange membrane, and water is separately introduced and discharged at the cathode and the anode, and other conditions are the same as in Example 2.

[0058] The removal rates of diatoms by the cathode-anode cooperative system of Example 2 and the cathode alone or anode alone of Comparative Example 1 are as follows: Figure 2 As shown, the removal rates of golden algae by the cathodic cooperative system of Example 2 and the single cathode or single anode of Comparative Example 1 are as follows: Figure 3 As shown. Figure 2 and Figure 3 It can be seen that within the 1-hour operation cycle, the removal rate of diatoms and golden algae in the effluent of the cathodic-anode synergistic system was maintained at about 100%, and the performance of the anode alone in removing diatoms and golden algae was better than that of the cathode alone; for golden algae, the removal rate of the cathodic-anode synergistic system was significantly higher than that of the anode alone and the cathode alone. Compared with the cathode or anode alone, the cathodic-anode synergistic technology showed higher removal efficiency and longer stability time for diatoms and golden algae, proving that the cathodic-anode synergistic technology has more efficient biological inactivation performance for ballast water.

[0059] Example 3

[0060] The cathode is an undoped activated carbon material, the anode is a sub-titanium oxide electrode, and other conditions are the same as those in Example 1.

[0061] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for treating ship ballast water by using an electrochemical cathode and an anode, characterized in that: The anode and cathode are placed in a static electrolysis cell containing ship ballast water or a flowing electrolysis cell containing ship ballast water, and oxygen or air diffuses 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. The active species produced at the cathode and anode act synergistically to inactivate organisms in the ballast water.

2. The method according to claim 1, characterized in that The active species generated by the electro-oxidation of seawater or chloride ions at the anode include one or more of hydroxyl radicals, chlorine radicals and ozone; the active species generated by the electro-reduction of oxygen at the cathode include one or more of hydroxyl radicals, singlet oxygen, hydrogen peroxide and superoxide radicals.

3. The method according to claim 1 or 2, characterized in that: The active species produced by the cathode electroreduction of oxygen undergo oxidation reaction at the anode and cathode interface or diffuse into the bulk solution to undergo oxidation reaction, and the oxidation reaction inactivates the organisms in the ballast water.

4. The method according to claim 3, characterized in that 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.

5. The method according to claim 4, characterized in that 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-titanium oxide electrode.

6. The method according to claim 5, characterized in that The preparation method of the boron-oxygen co-doped carbon nanotube electrode comprises the following steps: 1) placing carbon nanotubes in mixed acid for acidification treatment and then washing with water until neutrality to obtain acid-treated carbon nanotubes; 2) calcining the acid-treated carbon nanotubes and boric acid under a protective atmosphere to obtain boron-oxygen co-doped carbon nanotube powder; 3) Boron and oxygen co-doped carbon nanotube powder, Nafion membrane solution and water are mixed and then ultrasonically dispersed, and the dispersed catalyst is coated on a hydrophobic carbon cloth to obtain a boron and oxygen co-doped carbon nanotube cathode.

7. The method according to claim 6, characterized in that 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 temperature of the acidification treatment is 60-120° C., and the time of the acidification treatment is 0.5-6 hours; Step 2) The mass ratio of the acid-treated carbon nanotubes to boric acid is 1:2-13; the calcination temperature is 600-1000°C, and the calcination time is 0.5-5h; Step 3) The mass volume ratio of the boron-oxygen co-doped carbon nanotube powder, Nafion membrane solution and water is 10-30 mg: 180-220 μL: 1500-1700 μL; the ultrasonic dispersion time is 10-30 min.

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