Magnetic fields. Water to be treated is passed through a magnetic field of specified flux that is generated by ferromagnetic or electromagnetic devices. The biological and chemical effects of magnetic systems are not well understood, but it is thought that the organic and inorganic constituents of living organisms in the water are altered by the magnetic field.
Deoxygenation. Most potential aquatic nuisance species require oxygen to survive. When oxygen is removed from the water, many organisms (but not cysts, spores, or anaerobic bacteria) are killed. Some organisms that require oxygen can survive short periods of anoxia, but they are usually inactive under such conditions. Oxygen can be removed from water by purging with an inert gas or by binding oxygen to a chemical additive.
Biological techniques. Biological techniques to control unwanted species include the introduction of additional organisms that are predators, pathogens, or competitors of the species of concern. Such techniques have proven useful in the control of certain insect pests when the biocontrol species develops self-sustaining, reproducing populations. Biological treatment also includes the use of modern biotechnology methods to modify the genetics of the organism of concern.
Anti-fouling coatings. Anti-fouling coatings on hulls reduce biological fouling by contact toxicity, ablation or surface activity. The vast majority of coatings used today rely on toxicity or ablation, or a combination of the two. Surface-active systems are marketed as "fouling release" coatings, but their use is limited because they are expensive.
The committee's evaluations and details of the most promising technologies are discussed in the following sections.
Once the treatment problem was defined, the committee developed a list of candidate technologies, drawing in part on wastewater treatment methods. A treatment options query developed by the committee combined a list of technology requirements and capabilities with shipboard application considerations. On the basis of this questionnaire, technology vendors and research organizations were invited to provide data for typical shipboard treatment systems. These data were used by the committee in assessing candidate technologies. All technologies were required to meet safety and effectiveness criteria before being evaluated further. At the conclusion of this assessment, the candidate technologies were grouped into three categories: (1) promising options, (2) options with possible limited application, and (3) other options.