Nonindigenous species invasions from ship ballast-water discharges are a growing ecological problem in coastal and inland waters throughout the world. Several of these invasions have been very dramatic and have caused widespread change to marine and freshwater ecosystems, as well as significant damage to living resources and other water uses.

There is consensus among scientific communities and regulatory agencies that future nonindigenous species invasions should be prevented. The present means to prevent introduction of aquatic species is for ships to exchange ballast water in the mid ocean. In many cases, however, ocean exchange is neither possible nor practical because of the design or operation of the vessels, or because the vessels do not transit open ocean waters.

This study evaluates three ballast-treatment technologies—ultraviolet radiation (UV), thermal (heat), and acoustic (ultrasonics)—for potential application to secondary treatment of ballast water. The shipboard use and biological effectiveness of the three treatment technologies were evaluated against no-, 250-m m-, 100-m m-, and 25-m m-pretreatment filtration scenarios; at 1,200 and 8,000-gmp flow rates; and water intake temperature of 35-45 ºF (2-7 ºC). The specifications complement the shipboard tests currently underway by Northeast-Midwest Institute and the Lake Carriers’ Association in the Great Lakes Ballast Technology Demonstration Project.

The principle component of this study was a survey of manufacturers and vendors of secondary treatment technologies. Thirty-eight vendors were contacted and 15 vendors provided useful information relevant to the current state of the three technologies. Additional technology information and performance data were obtained from published information, as well as from researchers working with water and wastewater disinfection.

This report summarizes the current state of development of the three secondary treatment technologies, including predicated biological effectiveness against nonindigenous microorganisms, robustness of the equipment, safety issues, and environmental concerns about using the technology aboard commercial vessels.

The conclusion of this report is that UV is currently the technology best suited for secondary treatment of ballast water. UV treatment technology is well developed, has many vendors producing equipment for a variety of applications, and, of the three options examined, shows the best potential for shipboard trials.