Microbial disinfection of seawater using hydrodynamic cavitation

• Application of hydrodynamic cavitation for ballast water treatment has been studied.
• Different cavitating devices and their effectiveness in terms of disinfection and energy utilization was studied.
• Cavitation treatment can be effectively used as, “onboard ballast water treatment technology”.
• Hydrodynamic cavitation can be effectively used onboard with minimum maintenance and crew requirement.

Hydrodynamic cavitation has been effectively proven to be an efficient advanced oxidation process on an industrial scale. The utility of hydrodynamic cavitation for microbial disinfection of seawater has been reported in this work. Seawater is used as cooling water in refineries and nuclear power plants or as ballast water in the shipping industry. Various norms and regulations of the International Maritime Organization (IMO) make it compulsory for ship owners to treat the ballasting seawater before discharging it into the sea. Also, if the seawater is not properly treated, it causes biofouling which affects the performance of cooling tower and other heat transfer equipments. It has been observed through our study that, hydrodynamic cavitation can be effectively used for microbial disinfection of seawater. Effectiveness of different types of cavitating devices for the extent of disinfection was studied. It was conclusively proved that, slit type of geometry consumes 40% less energy compared to cylindrical geometry for similar extent of seawater disinfection. A combination of the conventional treatments of water disinfection such as chlorination and thermal treatment with hydrodynamic cavitation was found to increase the overall rate of disinfection significantly. Rate of reaction almost doubles when 5 ppm hypochlorite was used as disinfectant with the combination of cavitation compared to when only 5 ppm of hypochlorite was used. Similarly the rate of disinfection increases 2.5 times at 50 °C in combination with cavitation compared to when, only 50 °C was maintained and disinfection was carried out.