Ocean Ballast Water Treatment Tools

Currently, mid-ocean ballast water exchange or retaining all ballast onboard the ship are the only federally approved strategies for ballast water management. Any alternative treatment technology is still experimental and not yet approved for broad use on ships by the United States Coast Guard. Some potential management techniques include:

  • Filtration/separation of ballast water
  • Sterilization of ballast water by ozone, UV light, electric currents, or heat treatments
  • Chemical treatments (biocides)
  • Asphyxiation (removing oxygen from ballast water)
  • A combination of the methods above.

Over the last three years, researchers from SERC and the Maritime Environmental Resource Center (MERC) have worked together on the Cape Washington in Baltimore's harbor to help test prototype ballast water treatment systems designed to work on a full scale vessel. SERC’s role has been to evaluate the efficacy of ballast water treatment systems by conducting biological analysis of zooplankton and phytoplankton collected in the tanks. We functioned as an independent scientific collaborator to provide technical consultation on experimental and sampling designs used to test the efficacy of alternative ballast water treatment systems and in no way endorse any particular ballast water technology. In these experiments we compared the number of organisms in the tanks before and after the treatment system was run, and compared these results with results from untreated control tanks to evaluate the effectiveness of the treatment in killing or removing organisms. For a treatment system to be effective it must be able to reduce the number of plankton in the tank to an acceptable level.

Recently the U.S. Coast Guard proposed a new set of rules limiting the number of live zooplankton to fewer than 10 organisms per cubic meter (m3) (264 gallons). With these new rules in place, we needed to know how to detect a small number of plankton in a large ballast water tank. To answer this, Dr. Whitman Miller and collaborators developed a statistical model to estimate how much water needed to be tested in order to rigorously and accurately validate the effectiveness of a ballast water treatment system. Testing very large samples of water is difficult to manage on a ship, even though large samples may be necessary to detect sparse numbers of biota. An innovation of the model is that it can pool sample results over time and possibly across ships, making it easier to determine if treatment systems function as advertised and thus whether ships are actually compliant or not. Since analyzing samples larger than 7 cubic meters is difficult for most cargo ships, by taking multiple 7-cubic-meter samples, regulators could effectively raise the volume without overburdening the ships. Learn more about this research here.

NISBASE reference search on ballast water treatment

The Cape Washington at the Port of Baltimore

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