Is the oxygen content of the discharged water measured?

When SO₂ is dissolved in water, a reaction occurs whereby the sulphur dioxide is ionised to bisulphite and sulphite, which is then readily oxidized to sulphate in seawater containing oxygen [1].

Relevant chemistry

This process increases the Chemical Oxygen Demand, which could potentially have an adverse impact on aquatic systems. Using worse case scenarios Karle and Turner [1] evaluated how much dilution of wash water would be required to return oxygen levels to within 1% of those of the ambient water. Using different waters from full seawater to full freshwater and intermediate alkalinities/salinities, it was found that, other than for full open ocean water above 15oC, no further dilution was required if the pH of the water had already been corrected to within 0.2 of ambient.

As it known from various in-field tests and modelling of discharge plumes that the pH and oxygen of discharged water very rapidly returns to that of the surrounding water, especially when the vessels is underway, the IMO does not require dissolved oxygen to be monitored [13].