Ozonation products of bromine and chlorine in seawater aquaria

Abstract

During ozonation of seawater in closed marine systems, reduced chemical species such as bromide ion and, to a much lesser degree, chloride ion may be oxidized to a variety of potentially harmful products. Concentrations and stabilities of several of these products were measured for the artificial seawater aquarium.The Living Seas. In this facility, where bromide ion was not originally added, trace amounts are present from impurities in NaCl. The total bromine concentration of the system is 57 μM with the following speciation after 6 years of operation: 5 μM bromate ion, <0.4 μM hypobromite ion and 52 μM bromide ion. To model the evolution of the observed speciation of bromide in this system, pure aqueous solutions of NaBr, NaCl and a mix of the two were ozonated. The results obtained, together with existing kinetic data, were used to develop a computer model of ozone reactions with artificial seawater. By applying the model to The Living Seas, we can account for the presently observed speciation of bromine. We conclude that even in an artificial seawater system where bromide ion is not added, this trace impurity is the dominant species oxidized during ozonation.