Curtailing Aquatic Introductions
Sea Grant Scientist Evaluates an Array of Ballast Water Treatment Options
By Jeff Bowman
Such ballast water discharges have led to numerous harmful introductions of exotic species. Most notably, the zebra mussel (Dreissena polymorpha) and quagga mussel (D. rostriformis bugensis) were introduced from Europe into the Great Lakes by shipping through the St. Lawrence Seaway. Like many other sessile aquatic organisms, these similarlooking mussels have a free-swimming stage in their life cycle, which allows them to be easily transported in ballast water.
Once an invasive species such as the zebra mussel is established in its new home, it is nearly impossible to eradicate. Between 1989 and 2002, efforts to control zebra mussels, which were rapidly clogging sewage treatment plant intakes, stormwater outfalls and other structures, cost the Great Lakes region a conservatively estimated $1 billion. In October 2007, Washington’s first citations for illegally transporting zebra mussels were issued to two out-of-state trucking companies hauling large boats to the Pacific coast. Live zebra mussels were found attached to boats being transported by a hauler from Ontario, Canada, and another from Iowa.
A Range of Treatment Alternatives
Washington Sea Grant has made the control of zebra mussels and other invasive species a priority. WSG researcher and University of Washington Associate Professor Russ Herwig works on the development and testing of systems for sterilizing ballast water on large vessels. He and Jeff Cordell, a research scientist, at the UW’s School of Aquatic and Fishery Sciences, lead a group of scientists and students, formally known as the UW Ballast Water Research Team.
Disinfecting ballast water in a cost-effective and environmentally friendly manner is a daunting task. The most effective techniques often rely on chemicals (called biocides) to kill or inactivate the organisms and, as Herwig points out, biocide treatments need to be environmentally friendly — a challenge for any chemical.
Long-standing maritime record keeper Lloyd’s of London lists 20 emerging technologies intended to solve this problem. These technologies employ a wide range of techniques for sterilizing ballast water. Because each technique produces slightly different results, the decision to adopt any particular technology will depend in large part on the ballast water standards set forth by various governing bodies.
Currently, standards for ballast water are set at state, federal and international levels. Within Puget Sound, the Washington Department of Fish and Wildlife inspects vessels for compliance with current regulations, requiring vessels to exchange ballast water off the coast before entering the state’s waters. By having ships exchange ballast water offshore, it is hoped that any exotic species carried in ballast water will be diluted to levels that will prevent them from establishing new populations in Washington. The minimal level needed for establishment success is known as the "inoculation number" or the "propagule pressure." For most aquatic organisms, scientists do not know how many are required to create a successful invasion in a new environment.
"It is not clear whether an exchange alone removes enough organisms to push all species carried on a vessel to a number that will prevent an invasion," says Herwig. "Furthermore, the process is timeconsuming and can be dangerous to vessels, particularly on stormy seas." Because of the ship’s and crew’s safety concerns, commercial vessels are sometimes permitted to bypass the open ocean exchange and discharge unexchanged water into their destination port’s waters.
Recent treatment standards adopted but not yet enforced by the International Maritime Organization (IMO), an agency of the United Nations, will require near-complete eradication of all organisms in ballast water before it is discharged. A certain number of countries need to ratify the ballast water standards before they become "in force" by the international community. Meanwhile, California and Washington are moving ahead to adopt their own ballast water discharge standards since the United States does not have discharge standards. These strict requirements may favor the use of biocides. The use of biocides presents a huge challenge to developing an environmentally friendly ballast water treatment technique. "How do you kill the hardiest organisms in ships’ ballast without killing the most fragile organisms in the surrounding environment when the treated water is discharged?" asks Herwig.
One of the new technologies tested by Herwig and the Ballast Water Research Team uses ozone as a biocide. Ozone is commonly used to treat municipal water supplies and swimming pools in place of chlorine. The energy company BP expressed an early interest in treating ballast water on its tankers. Working with ballast water technology developer Nutech-03, BP installed a prototype ozone treatment system in the ballast tanks of an Alaskan oil tanker. The system generated ozone onboard the ship and dispersed it through diffusers similar to the air stones used in home aquariums. The team found that the effects of ozone throughout the treatment were not consistent. "Our results were very promising," recalls Herwig. "But the vendor and research team concluded that the use of diffusers in ballast tanks was not the best method for introducing ozone into ballast water."
Fortunately, the BP ship test did demonstrate the willingness of corporate partners to work with researchers toward solving the ballast water problem. So long as solutions are cost- and time-effective, ship owners and operators are generally willing to help.
Electrochlorination, UV Light and Vitamin K3
Herwig’s team is now testing additional technologies. One of the more promising is an electrochlorination system manufactured by Severn Trent De Nora of Sugarland, Texas. This technique takes advantage of a ship’s ability to produce the biocide sodium hypochlorite, commonly known as bleach, by passing an electric current through seawater. The added sodium hypochlorite disinfects the ballast water while the ship is in transit between ports. Before the ballast water is released, the disinfectant is detoxified by the addition of a neutralizing chemical. Although highly effective at reducing invasive species in ballast water, chlorination highlights the difficulties presented by several biocide agents. Even after the neutralizing treatment, some harmful disinfectant byproducts may be produced, albeit at very low concentrations that may not be of concern.
The Ballast Water Research Team has looked at other biocides that try to get around this problem by using chemicals with short half-lives — that is, degrade quickly in the environment. Vitamin K3, or menadione, for example, has been developed for use a ballast water biocide under the trade name SeaKleen® and manufactured by the firms Vitamar LLC and Garnett, Inc. It can be introduced at a toxic level and then allowed to degrade to a level safe for release while the ship is in transit. Unfortunately, the team found that SeaKleen® did not degrade quickly enough in the cold waters of the Pacific Northwest. In addition, while SeaKleen® was found to be effective on zooplankton and other large ballast water invaders, it may not be as effective on small ones such as bacteria and phytoplankton.
Some other technologies have proven effective at controlling ballast water invaders with little risk to the environment. Ultraviolet (UV) light is commonly used in hospitals and laboratories to kill bacteria. Large flow-through systems that pump ballast water past super-sized UV lamps on ships have proven effective at sterilizing ballast water, especially when combined with a filter that removes larger organisms. The Ballast Water Research Team was surprised to find that, over time, this technique reduced the number of bacteria and large ballast water invaders.
The problem with UV light is the regrowth of bacteria, reports Herwig. "To achieve the best results using UV light, water must be pumped through the system as it is brought aboard and as it is expelled from the vessel," he explains. Additional concerns have been raised about the durability of the large UV lamps used in these systems, which must endure constant vibration and be kept clean during long voyages. Despite these concerns, UV light treatment may emerge as the technology of choice for smalland medium-sized vessels if it is effective enough to pass strict IMO and other regulatory guidelines. As the current technologies continue to improve and new technologies emerge, Herwig and other members of the Ballast Water Research Team will continue to provide scientifically sound testing and development. "That’s what we do best and what’s put us ahead of programs in other states," says Herwig. "I work with a great team of scientists who are working together to solve an environmental problem, thanks to the continued support from Washington Sea Grant."
Contact David G. Gordon, Science Writer for Washington Sea Grant, for further information.