Ballast Tank Sediments

When a vessel takes on ballast water in shallow areas, resuspended sediment and the associated benthic organisms and resting stages are also taken onboard. Once inside a ballast tank, the sediments settle out of suspension and begins to accumulate. The volume of accumulated sediment present in a tank is a result of the ships ballast management practices, the type of ballast tanks involved and the time since the tanks were last cleaned in dry dock. During a ballast water sampling programme carried out in England and Wales, numerous dedicated ballast tanks of ships in dry dock (ferry, container, cruise ships) were entered and the sediment sampled (Lucas et al. 1999). The volumes of accumulated sediment were found to vary considerably within ballast tanks, between ballast tanks and between ships. Sediment accumulations varied from a few cm to more then 30 cm depth which translate to 10’s and even 100’s of tons of sediment in the ballast tanks of larger vessels. Although the sediment type varied between ships, most of the sediment found was fine mud with a mean particle size of < 20 μm.