Biology

Over the last 50 years there has been a significant increase in the size and number of vessels involved in international shipping. In addition to cargo, these vessels transport large quantities, often thousands of tons, of water as ballast to maintain proper buoyancy and stability. To load cargo, ballast water is pumped out of the ship. The aquatic organisms transported in the ballast water are introduced into this new environment. These biological invasions have resulted in infrastructure damage, toxic algal blooms, and the collapse of native coastal fisheries. As shipping has increased, so has the number and severity of ballast-water related biological invasions.

Zebra Mussels

The most devastating aquatic nuisance species, the zebra mussel was first discovered in the Great Lakes near Windsor, Canada in 1988. It was transported there in the ballast of a vessel arriving from the Black Sea. The effort to stop the spread of this mussel now costs Canada and the US (primarily utilities) hundreds of millions of dollars annually. Although the Great Lakes were initially the focal point for this issue, there are now thousands of similar stories around the world.

To limit the potential for future invasions, pending international regulations will require globally-trading ships to install a ballast water treatment system to eliminate the introduction of ballast water-transported organisms into port ecosystems. Specifically, the International Maritime Organization (IMO) passed regulations in February 2004. Member maritime nations including the Norway, US, Canada, Japan, Australia and the EU countries are in the process of developing national regulations to enforce this new international law. The IMO web site www.imo.org provides additional information about this issue.

Corrosion

The inside of a vessel ballast tank is one of the most corrosive environments on earth. Water, particularly salt water, acts as a catalyst for oxygen to turn steel into rust:

Water + Oxygen + Steel = Rust

Being that for the foreseeable future seafaring vessels will be made of steel, and water will be used as ballast, what can be done to decrease corrosion?

Since air is 21% oxygen, purging the air from ballast tank void spaces removes one parameter of the above equation.

Worse Case Scenario