Microbial disinfection of seawater using hydrodynamic cavitation Mandar P. Badve, Mihir N. Bhagat, Aniruddha B. Pandit ⇑ Department of Chemical Engineering, Institute of Chemical Technology, Mumbai 400 019, India article info Article history: Received 15 April 2015 Received in revised form 10 July 2015 Accepted 12 July 2015 Available online 13 July 2015 Keywords: Hydrodynamic cavitation Ballast water Water disinfection Seawater Chlorination abstract 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 bal- last 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 discharg- ing it into the sea. Also, if the seawater is not properly treated, it causes biofouling which affects the per- formance 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 com- pared to when, only 50 °C was maintained and disinfection was carried out. Ó 2015 Elsevier B.V. All rights reserved. 1. Introduction For the past 30 years there has been a remarkable growth in the reported work on an efficient treatment and water purification technique by all categories of users. The categories include munic- ipal, industrial, institutional, medical, commercial and residential. The increasingly broad range of the reported techniques for improving water quality has motivated the water treatment indus- try to refine existing techniques, combine different methods and explore new emerging water purification technologies. Similarly, seawater disinfection is equally important due to its applications in shipping industry and refineries. Ships use ballast water to provide stability and maneuverability during a voyage. Water is taken on at one port when the cargo is unloaded and usually discharged at another port when the ship receives a cargo. The local microorganisms, ranging in size (from viruses to large fish) living in the surrounding water or sediments, are taken on board with ballast water. There is a potential danger for the introduction of non-native organisms – called bioinvaders, alien species, nonindigenous species or exotic species – into the port of discharge. In order to avoid this problem; IMO has made it compulsory to all shipping companies to treat the water before discharging it into the sea again [1]. Unfortunately no single ballast water management technique has been able to remove all types of organisms from ballast tanks. A combination of different methods may prove to be more effective than one method alone, however little research has been conducted into this possibility. It is difficult to implement treatments because the ship owners are understand- ably reluctant to install technology that is expensive, unreliable or time consuming. When evaluating ballast water treatment options a number of general factors must be considered. The factors include cost, the effectiveness of the method, the footprint and the possible external risks, which the treatment may pose to human health and the environment during its enforcements. The monetary cost of a treatment method includes the cost of the equipment, the crew needed to operate the treatment equipment, the cost of the disinfectant chemicals and the time needed for the treatment. Many treatment methods require the ships be retro- fitted with the necessary equipment or in new ships these equip- ments included as an integral part in their design. Both of these options may be quite expensive. The ship’s crew members have many tasks to perform on a ship, thus, the crew that is needed to operate this additional treatment task may decrease the number http://dx.doi.org/10.1016/j.seppur.2015.07.020 1383-5866/Ó 2015 Elsevier B.V. All rights reserved. ⇑ Corresponding author. E-mail address: ab.pandit@ictmumbai.edu.in (A.B. Pandit). Separation and Purification Technology 151 (2015) 31–38 Contents lists available at ScienceDirect Separation and Purification Technology journal homepage: www.elsevier.com/locate/seppur