Treatment Of Ballast Water By Ultrasound And Its Enhanced Technology

With the development of marine transportation, more and more ships sail continually overthe world. Exchange of ship’s ballast water results in great threaten to the marine ecologicalenvironment and sustainable development. IMO （International Maritime Organization） clearlyputs forward to reduce and eliminate the hazards of harmful aquatic organisms throughcontrolling and management of ballast water discharge. At present, there are many singlemethods for ballast water treatment, such as，mechanical, physical and chemical，but they areall difficult to meet the standards on ships. So it is emergency to find an effective method forcontrolling the pollution of ballast water.Ultrasound technology is a new type of environment-friendly technology with gooddevelopment prospect. It integrates advanced oxidation, burning and supercritical oxidation inone process. It can change the reaction conditions, speed up the reaction rate and make somechemical reactions.According to the properties of the ballast water and technological properties of othertreatment processes, ultrasound and its enhanced technology were proposed to treat the ballastwater. In this thesis, it focused on the chlorella removal effect under the ultrasonic parametersand other factors. Based on the provisions of D-2, ballast water was prepared by artificialseawater with chlorella.The experiment results showed that the removal efficiency increased under the condition ofconstant power and frequency with the irradiation time extending and the best duration timewas6min.As the increase of power, the effect trends to saturation and90W was chosen forthe subsequent experiments. In low frequency range, the chlorella removal efficiency is notobviously different.The enhancement of ultrasound on coagulation was investigated. The results showed that ithad different coagulation effects on chlorella for FeCl3，PAC andAl2（SO4）3separately. Withthe same concentration, it was the highest algae removal rates for PAC. It significantlyincreased the algae removal rate by20%with ultrasound at a PAC coagulant dosage of40mg/L.The ultrasonic enhancement was relatively stable at different frequencies and theoptimal work power was90W with the time of30s. In the end, the results showed that the US/H₂O₂will exist some synergetic effect whenthe concentration of H₂O₂is less than1.5mmol/L.The best algae removal could be achievedwith neutral pH.