Study On The Inactivation Mechanism Of Photo-fenton In-situ Coupling System On Ballast Water Bacterial Forces

Seaborne trade is the main way of freight,and in order to ensure the stability and operational safety of ships in the course of traveling.It has been estimated that 10-30billion tons of ballast water which contains a wide variety of biota is transferred across the world annually.Species living in ballast water enter new environments and cause biological invasions,posing a serious threat to the marine environment.Therefore,pressure is required.The tank water is thoroughly disinfected.Ballast water sterilization is often realized with UV irradiation,chlorination,ozonation and electrochemical process.However,UV irradiation usually needs to consider the re-colonization of bacteria.Ozonation has the problems of high energy consumption and corrosion of the cabin.Electrochemical methods to produce sodium hypochlorite（Na Cl O）for the sterilization also suffer from high energy input and explosive H₂ gas as byproducts.In this scenario,advanced oxidative process（AOPs）based on hydroxyl radicals（·OH）formation has been considered as alternative technology for ballast water sterilization,due to the strong oxidation characteristics of·OH which has been proved to possess the ability to inactivate various kinds of microorganisms even in the seawater with high salinity.However,all of the identified methods require external high energy input,which lacks of sustainability.Meanwhile,Fenton system is well-established as one of the most powerful technology to generate·OH using H₂O₂as the oxidants in the presence of suitable catalysts.However,the high costs of production,transportation and storage of H₂O₂ significantly limits its sustainable application.Therefore,the work of this thesis is to find an environmentally friendly ballast water disinfection method and study its sterilization mechanism.The main research contents of this study are as follows:（1）In this study,a conceptual in-situ photo-Fenton system without additional oxidants was first established for ballast water sterilization.As an example,pyromellitic acid diimine（PDI）-modified g-C₃N₄ was utilized as a photocatalyst to produce H₂O₂,which was in-situ activated by Fe（II）to produce·OH for deep oxidation.Vibrio alginolyticus（V.alginolyticus）grown in seawater was used as the ballast water model bacteria in the inactivation experiment.Marine bacteria V.alginolyticus（7 log）in ballast seawater was totally inactivated within 35 min of visible light irradiation.Simultaneous bacterial inactivation and H₂O₂ production was monitored to explore the in-situ coupling mechanism,and·OH instead of H₂O₂ was determined to be the dominant reactive species for bacteria inactivation.The effect of seawater parameters（such as salinity,p H and dissolved oxygen）on the inactivation efficiency was also studied.In addition,the bacterial inactivation mechanisms in terms of cell membrane rapture,intracellular enzyme activity,and total protein change were clarified.The organic matter release profile during bacterial lysis was probed by fluorescence EEM technology,which exhibited minimal acute toxicity and impacts on the marine environment.This work not only advances a potential external oxidant-free system for on-board ballast water sterilization using sustainable solar energy,but also create avenue for exploring bacterial inactivation mechanisms in seawater.（2）Firstly,the g-C₃N₄/Fe OOH photocatalytic material was synthesized by the co-precipitation method.Under the irradiation of visible light,a small amount of H₂O₂is added to form an optical Fenton system.Using V.alginolyticus as a model strain,the system can completely kill 10⁷cfu/m L bacteria within 35 minutes.Similarly,it is determined that·OH is the main reactive species for bacterial inactivation,and it also has a good bactericidal effect under neutral p H conditions.Moreover,the photocatalytic material has good stability.