Tank Wash Water Discharge (MEPC 108)
Tank Water is also oily water. Tank water is usually produced by tankers washing out their cargo tanks between cargoes. After a vessel unloads it will return back to open sea and ‘wash’ its tanks out using sea water. This process normally takes a few days and the slop tanks then need to be emptied.
This discharge falls under MEPC.108(49) which means vessels can only discharge while underway (moving) at a rate of 30ppm per nautical mile or An accumulated volume exceeding 1/30,000 of the total volume of previous journey’s cargo.
The tank water can also be discharged via slop receptions in ports but this can be expensive and normally reserved when the ppm value is too large to discharge through the Oil Discharge Monitoring Equipment (ODME).
ODME is based on the measurement of oil content in the ballast and tank water, to measure conformance with regulations. The apparatus is equipped with a GPS, data recording functionality, an oil content meter and a flow meter.