Research Technical Report

Ballast Water Deoxygenation Can Prevent Species Introductions While Reducing Ship Corrosion

Tamburri, M.N., K. Wasson and M. Matsuda (2001)

2nd International Conference on Marine Bioinvasions

ABSTRACT

One of the most important mechanisms for the introduction of aquatic nuisance species is transport in ship ballast waters. Although several ballast tank treatments to prevent transport of aquatic organisms appear promising, all existing approaches will result in significant costs to the shipping industry. Our presentation will describe a treatment that can dramatically reduce the survivorship of most organisms found in ballast waters while providing economic benefits to ship owners.

Purging of oxygen from ballast tanks with nitrogen was recently found to be a cost-effective technique for reducing corrosion. This new deoxygenation technology decreases the rate of rusting to 10% of untreated ballast tanks and represents a significant saving for ship owners when compared to other corrosion prevention approaches currently available. Recognizing the potential benefits of this technique for reducing the survivorship of many organisms found in ballast waters, we tested the tolerance of larvae from known invasive invertebrate species (Ficopomatus enigmaticus, Dreissena polymorpha, Carcinus meanas) to oxygen levels found in nitrogen treated ballast tanks, and detected significant levels of mortality (see Figure below). Two separate literature reviews of oxygen tolerance for various aquatic species further support the conclusion that few organisms will be able to withstand extended periods of exposure to deoxygenated ballast water.

>Successful ballast water treatment technologies should meet the following important criteria: 1) effective at killing potentially damaging invaders, 2) safe for shipboard crew, 3) environmentally benign, and 4) affordable for ship owners. Deoxygenation appears to partially meet the first criterion by being highly effective at killing animal invaders (larval, juvenile and adult forms) but may be less effective for other taxa, particularly those adapted to low oxygen environments or with resistant stages such as cysts. Second, with proper equipment and training, nitrogen poses no major threats to crew safety. Third, nitrogen is relatively benign when discharged. Hypoxic ballast water would likely mix rapidly with shallow oxygenated water in harbors, and therefore create little danger for native estuarine organisms, which can withstand brief reductions in oxygen levels. Finally, ballast water admirably meets the fourth criterion. Rather than an added expense for ship owners, it actually represents a net saving, due to the significant decrease in corrosion.

Recently, the National Research Council evaluated ten candidate technologies for shipboard treatment of ballast water and concluded that intensive filtration, use of biocides, and thermal treatments held the most promise. Deoxygenation did not receive high priority, because of its failure to kill organisms resistant to hypoxia. While other ballast water treatment options may be more comprehensively effective, they come at greater environmental and financial cost. For instance, biocides may be hazardous for the crew as well as for native organisms in the vicinity of the ballast discharge. Moreover, these techniques come at a significant price for ship owners. Clearly, until mandated to do so, the shipping industry is unlikely to voluntarily install expensive ballast water treatment technologies. In contrast, we propose that widespread voluntary adoption of nitrogen treatment may result if the economic benefits for controlling corrosion become well known. Ballast water deoxygenation certainly deserves further exploration as a potential high priority treatment option, at least until international legislation mandates total mortality of ballast water organisms. While ballast water treatment has been controversial, raising conflicts between environmentalists and industry, nitrogen treatment represents a working solution that should appeal to both parties.

In summary, nitrogen treatment, by significantly reducing the level of oxygen in ballast tanks, both reduces corrosion and will cause substantial mortality of a large proportion of transported organisms. As such, it represents a rare example of a technology that simultaneously has benefits for marine conservation and industry.

Mean percent survival (± S.D.) of Ficopomatus enigmaticus (polychaete), Carcinus meanas (green crab), and Dreissena polymorpha (zebra mussel) larvae after 2 or 3 days of being held in water open to air (normoxia) and in water where oxygen was removed by purging with nitrogen gas (hypoxia).

Reference:

National Research Council. 1996. Stemming the tide: controlling introductions of nonindigenous species by ship's ballast water. National Academy Press, Washington, D.C., 141 pp.

Key words: ballast water, corrosion, deoxygenation, hypoxia, oxygen tolerance

Cite as: Tamburri, M.N, K. Wasson, Matsuda, M. 2001. Abstract, 2nd International Conference on Marine Bioinvasions.

See 2002 Journal Article for additional information