Ozone Residual Measurements for Aquaculture

Residual Ozone Measurements

Residual ozone in fresh water can be measured by the indigo colorimetric method, which is based on the decolorization of indigo by ozone (American Public Health Association, 1989). The decrease in light absorbance is linear with increasing concentration, and can be measured by a spectrophotometer at a wavelength of 600 nm. Because of the rapid reaction of ozone with bromide in seawater, it is not possible to measure dissolved ozone directly. Methods detecting the total residual oxidants (TRO) formed by ozone have been applied, including the DPD (N, N-diethyl-p-phenylenediamine) method and the iodometric method. As a surrogate parameter, the redox-potential is used for monitoring the oxidizing power of ozone and its oxidants in many practical applications. However, the absence of a linear relationship between residual ozone concentration and redox-potential is a disadvantage of this method.