| Due to the rapid globalization of the economy,shipping is now the main mode of global commercial transport.As a result,large amounts of ballast water are transferred between global waters every year,and the alien organisms carried by ships’ ballast water have become the most important pathway for species invasion.To prevent the adverse effects of alien species,the International Convention for the Control and Management of Ships’ Ballast Water and Sediments,adopted by the International Maritime Organization(IMO)in 2004,requires ballast water to be treated before discharge,strictly ensuring that the discharged ballast water does not threaten the marine environment.This thesis proposes a method for treating ship ballast water using microbubble technology.The collapse of microbubbles in water generates a localized high temperature and pressure shock wave,and this high density of energy further encourages the production of oxidizing radicals in the water,which gives the microbubbles a certain degree of microbial inactivation.The efficient generation of microbubbles is achieved by hydraulic cavitation,and the effect of cavitation microbubbles and ozone microbubbles on the treatment of ship ballast water is investigated with marine microalgae as an indicator species.The main work completed in the thesis is as follows:(1)The mechanism of microbubble generation by hydraulic cavitation was investigated by fluid finite element simulation to investigate the influence of the generator structure and pressure on the bubble generation process.The simulation results show that for the same inlet pressure,the longer and narrower the flow channel in front of the outlet,the more the cavitation bubbles are generated;while for the same flow channel structure,the higher the inlet pressure,the more the cavitation bubbles are generated.(2)An experimental microbubble ship ballast water treatment system was established based on the hydraulic cavitation method,which was able to generate microbubbles efficiently and achieve continuous treatment on a laboratory scale through circulation piping.The algae inactivation performance of the cavitation microbubble treatment system was investigated using Platymonas subcordiformis,Nitzschia closterium and Phaeodactylum tricornutum as target organisms,and the effects of the initial biological density and continuous storage of microalgae on the inactivation effect were investigated.This study demonstrated the effectiveness of microbubble technology in inactivating some marine planktonic microalgae,but the duration of treatment time required was long,and the treatment time required increased with higher biological density,and it was difficult to inhibit the growth of microalgae in the long term after cavitation microbubble treatment.(3)To address the problems of slow cavitation microbubble treatment efficiency and unsuitability for long-term storage,and to take into account the principles of biological effectiveness and environmental acceptability,microbubble ozone treatment technology was injected into the experimental system in trace amounts to investigate the sustained treatment effect,post-treatment water quality changes and biomorphological changes of the treated species.The algae control performance of the two microbubble treatment technologies was compared and the advantages and disadvantages of cavitation and ozone microbubble treatment were analyzed.The experimental results show that the ozone injection significantly enhanced the inactivation efficiency of the microbubbles,and that the treated water quality was in good condition with only a small number of residual oxides produced,and also inhibited the growth of microalgae effectively and for a long period of time,fully meeting the Ballast Water Convention discharge standards. |
PDF Full Text Request