Optimizing ballast water management: An evaluation of ballast water treatment system performance in challenging water conditions

The movement of ballast water is a major pathway for introducing aquatic invasive species. Ballast water management systems (BWMS) aim to reduce species introductions, but their performance varies under challenging water quality conditions. This study assessed BWMS performance in a freshwater port with impaired water quality by comparing harbour conditions to challenge water criteria for type approval testing defined by the International Maritime Organization and U.S. Environmental Protection Agency, and by analyzing paired harbour uptake and ballast discharge samples. Of 18 harbour samples, 67% approached or exceeded challenge water criteria for ≥50 μm organism abundance, while 22% and 11% exceeded criteria for dissolved organic carbon and total suspended solids. All nine discharge samples met limits for small organisms (≥10 to 99% reduction from uptake levels. Abundance of larger organisms in discharge was affected by uptake water quality (ultraviolet transmittance and organism abundance), and BWMS treatment type/filter size. The findings suggest that raising challenge test criteria may improve BWMS reliability across environmental conditions.