6.1 PH There is some concern that sending seawater back into the ocean with acidic sulphurcontaining wastewater is harmful enough to the marine ecosystem that it “renders the technology impractical” (Kehoe et al., 2010). The washwater from a seawater scrubber unit can have a pH as low as 3; therefore, to avoid a negative impact on ecosystems and potential corrosion issues, the washwater must be further neutralized and diluted with additional seawater to increase the pH level to greater than 6.5, as required under the IMO EGCS Guidelines. Alternatively, the IMO Guidelines allow the pH limit for the discharge to be determined during commissioning by measuring pH in the plume at a distance of 4 m from the discharge point, and determining the discharge pH that corresponds to a plume pH equal or exceeding a value of 6.5. This alternative compliance method of measuring the pH is consistent with EPA CORMIX principles where 4 m is considered the boundary of the initial mixing zone between water discharged overboard and water surrounding the vessel (Jirka,1996 and EGCSA, 2010). Low pH water can adversely impact marine organisms such as shellfish and, as many organisms are only able to survive when environmental conditions are stable, a decrease in pH may be a risk for those organisms. The IMO indicates that, in general, no environmental harm is considered to arise from short-term exposure of seawater with pH values as low as 6.5 (Hassellöv and Turner, 2007). A different pH discharge criteria is applied for moving vessels: during maneuvering and transit, a maximum difference of 2 pH units is allowed between the ship’s inlet and overboard discharge. As previously noted, for vessels underway, the mixing of discharged washwater with fresh seawater by the turbulence of the ship’s wake is highly effective, so that recovery of the pH to that of the surrounding water is rapidly achieved (EGCSA, 2010). | ||