Scrubber discharge water criteria
The MEPC.340(77) section 10 criteria set for exhaust gas cleaning system discharge water: pH, PAH, turbidity, nitrate, additives and residue handling.
Discharge water criteria for an exhaust gas cleaning system are set in section 10 of resolution MEPC.340(77), and they are the part of the regime under the most active review. Four parameters carry numeric limits: pH, polycyclic aromatic hydrocarbons measured as phenanthrene equivalent, turbidity, and nitrate.
Three of the four are normalised or referenced rather than absolute. The PAH limit of 50 micrograms per litre above inlet applies at a specific discharge water flow rate of 45 tonnes per megawatt hour and scales inversely with flow down to 25 at 90 t/MWh and up to 2,250 below 1 t/MWh. The nitrate limit is the greater of the figure associated with a 12 per cent removal of NOx from the exhaust or 60 mg/l normalised to the same 45 t/MWh. Only pH is stated directly, at not lower than 6.5 measured at the overboard discharge.
The full article will set out each criterion with its paragraph number, the instrument accuracy and recording frequency requirements, the additive assessment route, the residue prohibition on discharge and on board incineration, and how the criteria feed a coastal State’s own discharge restriction decision.