Effect And Simulation Of Ship Ballast Water UV Collaborative Electrochemically In-Situ H₂O₂/ClO Production For Algae Inactivation

Ship ballast water is an important factor causing migration and invasion of marine microorganisms,thereby becoming an important topic attracting much attention.In engineering systems for ballast water sterilization,hydrogen evolution of cathode material in electrolytic chlorination system has always been a key problem to be solved.For this reason,researching carbon-matrix materials for dielectron oxygen reduction（2e-ORR）towards to H₂O₂ is as the purpose,further establishing electrochemical in-situ H₂O₂/ClO^-generation system as the core,collaboratively constructing UV system killing algae in ship ballast water.By means of experimental research and multi-physics coupling modeling,the following contents are obtained.Based on the principle of electrochemical and photoelectrochemical dielectron-oxygen reduction（2e-ORR）towards to H₂O₂,two kinds of carbon-matrix composites electrodes are developed for electrochemical and photoelectrochemical in-situ H₂O₂ production in order.Using graphene-like carbon nitride（t-g-C₃N₄）formed after strong acid treatment as the active component,graphite felt（GF）as the substrate and polyvinylpyrrolidone（PVP）as the stabilizer,a novel t-g-C₃N₄ composite electrode was synthesized by electrodeposition for electrochemical H₂O₂ production.High power transmission electron microscopy,Raman spectroscopy,X-ray photoelectron spectroscopy and electrochemical workstation analyzed and obtains the structure-activity relationship of composite electrodes.The optimized electrode can produce hydrogen peroxide efficiently in simulated fresh water of p H of 1-12,artificial seawater of p H of 7.8,and real seawater of p H of 8.2.Current efficiency of the electrode under the above environments is 93%-98%,82.5%and 82%,at the optimal macroscopic current density of 20 m A/cm².Additionally,Cu₂O/t-g-C₃N₄ as the active components,a Cu₂O/t-g-C₃N₄composite electrode was further prepared by electrodeposition for photoelectrochemical H₂O₂ production.Under the irradiation of visible light emitting diode（LED）,current efficiency of the electrode in the actual seawater for H₂O₂ generation reaches 99.4%.By means of high power transmission electron microscopy,X-ray photoelectron spectroscopy,ultraviolet photoelectron spectroscopy,photoemission spectrum,UV-visible diffuse reflection spectrum and electrochemical workstation,obtained band gap of the electrode is 0.98 e V,and cut-off wavelength of visible light absorption is 700 nm.Through the coupling of the Electric Field,the Flow Field and the Chemical Concentration Field,editing custom functions into COMSOL,a cathode system model of three-dimensional（3D）porous electrode for in-situ H₂O₂ production was constructed.The model predicts potential principle of H₂O₂ reaction in the simulated freshwater environments of p H of 1-12,solving local current density and potential inside the 3D perforated electrode.Furthermore,t-g-C₃N₄/PVP/GF composite electrode was scale-up prepared and optimized.Coupled with Ti-based electrode,a five-chamber continuous flow electrochemical system for in-situ H₂O₂/ClO^-production was established,and a complete 3D electrochemical system model was further constructed by multi-physics coupling.Capacity ratios of H₂O₂and ClO-as the optimization objectives,COMSOL carried out sensitivity analysis on various parameters,such as electrode size,effective size of cathode and anode chambers and film thickness,optimizing a electrochemical reaction system of the optimal structure.Introducing the concept of the Dilute materials Concentration Field,combined with numerical modeling standard of the ISO（ISO 23152:2021）for UV system design and optimization,a 3D model of UV collaborative H₂O₂/ClO^-killing algae was constructed.Custom functions are introduced into the model to calculate thresholds required for individual algae inactivation under different conditions.Thresholds of UV light dose,H₂O₂ and ClO^-concentrations dose of UV,H₂O₂ and ClO^-killing algae independently,are 0.82 m J/cm²,0.0116 s·mol/L and 0.00755 s·mol/L,respectively.Thresholds of ClO^-concentration dose and UV light dose of ClO^-/UV killing algae are 0.0058 s·mol/L and 0.1 m J/cm².Thresholds of H₂O₂ concentration dose and UV light dose of H₂O₂/UV killing algae are 0.009 s·mol/L and 0.68 m J/cm².Thresholds of H₂O₂ and ClO^-concentrations dose of ClO^-/H₂O₂ killing algae are 1.0e-5 s·mol/L and 2.8e-5s·mol/L.At the meanwhile,under UV incident intensity of 330μW/cm² and the hydraulic retention time of 5 s,the above thresholds of UV/H₂O₂ and UV/ClO^-acting on microalgae are used as the conditions for particle velocity initialization.The model reverse-predicts the online dosages of hydrogen peroxide and hypochlorite to meet the IMO and the USCG inactivation standards on microorganisms of the size between 10μm and 50μm.