Abstract
Ozonation of sea water for biofouling control is being utilized in desalination processes, heat exchange systems, as well as in salt water aquariums. The chemistry of ozone in sea water is much more complex than in fresh water due to the high concentration of easily oxidizable, ozone-demanding species and the formation of secondary oxidants. The major secondary oxidant is bromine in the form of hypobromite and hypobromous acid (BrO−/HOBr) which are formed by oxidation of the bromide ion (Br−), naturally found in sea water in concentrations of 65 mg/L. HOBr can react again with ozone to return Br−, resulting in accelerated decomposition of ozone, or to form bromate (BrO3−) The BrO− ion is known to interfere with the measurement of residual ozone in sea water, so it is important that the feed gas conditions, solution pH, and the hypobromous and bromate concentrations be reported to quantify the amount of ozone introduced into a system.
In 0.5 N NaCl and sea water solutions, ozone appears to stabilize the passivity of passivating metals, but susceptibility to crevice corrosion appears to increase in the same environments. The effect of BrO−/HOBr on the corrosion of metals in sea water is believed to be similar to chlorine and ozone, in that it acts as a strong oxidizer. However, it is not certain whether BrO−/HOBr and BrO3− have any damaging effects on protective metal films.
