Computational Fluid Dynamics Analysis of Ballast Water Treatment System Design

The effective management of ships’ ballast water is critical for preventing the spread of invasive species. Despite advancements in UV-based ballast water treatment systems (BWTSs), achieving a uniform flow distribution within UV reactors (UVRs) remains challenging due to the spatial constraints of ships. This study employs computational fluid dynamics (CFD) to analyze turbulent seawater flow in a real-case BWTS installed on a self-discharging bulk carrier. The flow uniformity at UVR inlets and the volume flow rate (Q) distribution between parallel reactors are evaluated at nominal flow rates of 1000, 1900, and 2000 ${\mathrm{m}}^3/\mathrm{h}$. The results indicate significant disparities at maximum capacity (2000 ${\mathrm{m}}^3/\mathrm{h}$), with the starboard configuration exceeding the recommended Q per UVR by 4.95%, thus requiring operational adjustments. Six geometric modifications are assessed, revealing that optimized pipeline bends and T-junction designs (e.g., ST_3 and ST_4) improve velocity uniformity and maintain the relative Q distribution errors below 8.5%. This study identifies vortical structures generated by sharp geometrical transitions as primary contributors to flow instability. By bridging CFD insights with practical engineering constraints, this work provides feasible recommendations for retrofitting existing BWTSs and designing future systems, ultimately enhancing treatment efficacy, reducing UV lamp wear, and supporting compliance with International Maritime Organization (IMO) standards.