To Filter, or Not to Filter: That Is the Question

Ballast water treatment technologies must meet stringent performance standards at the point of discharge. Currently, no matter the technology used, a filtration step appears crucial to remove large organisms present in the intake water, to ensure a minimum but still sufficient residual biocide or oxidant concentration, and to decrease the sediment load. Organisms potentially able to survive the initial treatment are those benefiting from a behavioral or morphological refuge allowing them to temporarily escape from lethal or stressful environmental conditions, or those present in such unusually high concentrations that the treatment system is overwhelmed, or a combination of both conditions. Many different species have evolved a capacity to endure stressful environments, such as low dissolved oxygen concentration, desiccation, or toxins, by isolating themselves inside impermeable shells (e.g., mussels, clams) or organic coatings (e.g., egg capsules, cysts), or by burying themselves in sediments (e.g., bacteria, worms).