Depending on the type of biocide, ship ballast water treated with biocides must be detoxified using methods that avoid discharging unwanted concentrations of residual biocide and toxic byproducts into the environment (Chattopadhyay et al. 2004). Many biocide applications for ballast water treatment require chemical neutralization prior to discharge. Most ships neutralize treated ballast water before discharge, but some rely on minimum hold times to provide an opportunity for sufficient degradation of residuals (Lloyd’s Register 2010). Water temperature and salinity affect the rate at which chemical biocides function and break down (Albert et. al. 2010).
Prior Applications: Biocides are widely used in the health, food, and water treatment industries. Biocides have been studied as a means to prevent ANS introductions in ballast water via international shipping (Chattopadhyay et al. 2004).
General Effectiveness: Biocides used in industry can be effective at controlling ANS when used properly. Factors that influence the efficacy of biocides on microorganisms and other aquatic species include the biocide’s chemical properties, the size and characteristics of the organism, biocide concentration, treatment/application process, contact time, and water quality (e.g., salinity, pH, temperature, oxygen content) (Chattopadhyay et al. 2004).
The U.S. Coast Guard (USGS) Research and Development Center conducted a qualitative assessment of potential ballast water biocides and their effect on different organisms (Table 2). For this qualitative assessment, this evaluation of biocide effectiveness does not consider conditions under which the biocide was tested; rather the evaluation considers only whether the outcome of the study resulted in the desired effect. Except for otherwise noted, the information on biocide effectiveness referenced in this fact sheet was obtained from literature search conducted to complete USGS’s assessment and was not the result of scientific research targeted specifically for ballast water treatment or use in an open flowing system, and must be used cautiously (Chattopadhyay et al. 2004).
Operating Constraints: Biocides have specific use restrictions and requirements, which are found on the product label. The following are only a few of the numerous operating constraints that would require consideration. To be effective, target concentrations and specific contact times must be obtained throughout the water column. Additionally, depending on the selected biocide, it may be necessary to deactivate or neutralize the biocide to avoid killing non-target organisms upon release of treated water, or downstream of a treatment area. Certain biocides may create toxic by-products, persist in the environment and accumulate in sediment, making sediment reuse or disposal problematic.
A compilation of the physiochemical properties, treatment efficacy against target organisms, environmental acceptability, and other vendor information for many biocides can be found in Chattopadhyay et al. (2004).
