Development of a hydrodynamic static mixer for mixing chemicals in ballast water treatment systems

Abstract The movement of non-indigenous aquatic species (up to about 6000 species) along with ballast water into foreign countries during the shipping process poses concerns to human and environmental health as well as aquatic biodiversity. The International Maritime Organization (IMO) is expected to impose tighter regulations on ballast water discharges in the near future, and consequently, the development of more efficient ballast water treatment processes is required. In this study, the hydrodynamic performance of a static mixer in a ballast system for the complete mixing of injected chemicals and ballast water flowing in the main pipe was numerically investigated. Through several steps (design of mixer shape using numerical methods, CFD simulations, and validation tests), the performance of the static mixer was evaluated. The CFD simulation results showed that the target fluid (water + chemical) was completely mixed at a distance equal to 8 times the pipe diameter downstream of the mixer outlet, and the mixing quality was about 95%. Furthermore, the results of the CFD simulations and the validation tests were in agreement. The results of this study suggest that the use of a static mixer in the disinfection and neutralization system stabilizes the system and minimizes the amount of chemicals consumed.