general, automated monitoring method currently available that could be easily applied on board ship.
Biocide treatment units are relatively simple, although their size could be an issue when retrofitting existing vessels. Units can be designed to require little maintenance, and the greatest burden to the crew would be the filling and monitoring of bulk solution tanks.
Chemical addition for inactivation of micro-organisms has been reviewed recently (Carlton et al., 1995). In general this approach has been dismissed for many reasons including the following:
reluctance to add any compound to water that might be discharged back to the ocean
uncertain effectiveness of biocides in achieving inactivation of the target organism(s)
handling of chemicals on board ship
compliance with discharge regulations for such chemicals in certain areas of the world
Although these concerns are real, they can be addressed by appropriate research, development, and demonstration activities. Addition of selected biocides may be the most economic solution to achieving the desired goal of inactivating target species.
The safety issues associated with handling chemicals on board a ship may be of concern. Ships routinely carry hazardous industrial compounds and lubricants because they are needed for ship operations. Personnel responsible for handling these compounds are well trained and would be able to adapt to handling other materials without serious constraints. The concentrations of chemicals needed to treat ballast water should be small, and storage requirements may be insignificant. The residual chemicals left in a ship's ballast tanks following treatment and the possibility of corrosion of piping, pumps, and structure need to be evaluated.
Decades of studies have demonstrated that, in general, chlorine is an effective biocide. Its specific application for ballast water will require data on the required concentrations and contact times for different categories of organisms—ranging from bacteria and viruses to adult crustaceans and fish—and relative to water flow rates and/or tank volume and water residence time.
Electrolytic chlorination creates active chlorine by passing an electrical current through water containing chloride ions. The chloride ions in brackish water and seawater are used in this process. Chlorination units are comparatively small and used on many ships for biofouling control of seawater cooling systems. A