Sewage Treatment Plant

A marine sewage treatment plant processes a vessel's black and grey water on board, breaking down and disinfecting waste before it is discharged, so a vessel is not required to hold sewage for shore disposal alone. What a discharge is required to meet, treatment standard, monitoring, or simply holding for shore reception, depends on where the vessel operates and under which MARPOL Annex IV provisions it is certified, a class and flag-state matter decided per vessel. Most designs use a biological or aeration stage to break down waste before a final disinfection step, and the unit is sized to the number of persons on board it is certified to serve.