Treatment of Ballast Water on Board Ships

Abstract

The global transport of ballast water in ocean-going ships contributes substantially to the spread of aquatic invasive species, with serious consequences to local ecosystems. Therefore, the treatment of ballast water prior to discharge will soon become mandatory. Within the last decade, several dozen ballast water treatment systems have been developed. Most of them employ chemical oxidants, namely chlorine, ozone, and peracetic acid. In the bromine-rich marine water the chemistry of these primary oxidants is mainly characterized by the secondary oxidant hybobromite/hypobromous acid. As a consequence, brominated disinfection by-products are formed. Tribromomethane and tribromoacetic acid are frequently found in concentration >100 µg/L, followed by dibromochloromethane, dibromoacetic acid, and dibromoacetonitrile (10–100 µg/L). As all of these substances are associated with genotoxicity, carcinogenicity or other long-term toxicity, close attention needs to be paid to the prevention of unacceptable exposure of humans during ballast water treatment on board ships.