Sea water is mainly basic (pH=8.0-8.5) and as a result chlorine is not a wise choice for disinfecting it. That’s due to the fact that chlorine solution in water is only able to act as a disinfectant in the form of hypochlorous acid (HOCL) and concentration of hypochlorous acid reaches its maximum at the pH of 5 to 7. However, performance of chlorine dioxide is not a function of pH and consequently in very low concentrations (less than 0.2ppm) is capable of being used for sea water disinfection.
Bromide ion (Br–) is one of salts prevalent in sea water. Amount of this ion in Persian Gulf’s water is around 100 mg/liter. Chlorine changes Bromide ion into Bromate (BrO3–) which is carcinogenic and its maximum allowed limit is 10 mg/liter (10ppb). Moreover, bromide, adjacent to chlorine, is able to generate bromoform and other organic bromide compounds which are categorized as THMs and are also carcinogenic.