DISPOSAL OF RESIDUES ON BOARD
Both solid and liquid residues are produced on board. The latter are classified as:
The two drainage systems are differentiated to avoid the flow of black water to other areas.
Black water can transmit a number of illnesses such as cholera, typhoid fever and dysentery; while grey water, although less dangerous from a health point of view, can be harmful to the sea environment due to impurities, especially those derived from the kitchen, rich in fats, and the laundry, with the remains of detergents, which is why the disposal of these substances is governed by international conventions (prohibited in port areas and coastal waters beyond 12 miles in the case of sewage water).
The drainage system for residual water should be totally independent to the drinking water circuit, in order to prevent contamination.
Solid residues are those waste materials that, because of their size or nature, cannot be eliminated alongside residual water. Originating in the kitchen and cabins (leftovers, wrappers, cans, magazines…), work areas (brushes, rags, paint tins, grease…) and the engine room (engine parts, lubricants and oil…).
Health wise, the most dangerous substances are food leftovers and wrappers, as their presence could attract insects and rats. The rest of the waste poses an environmental threat, and as such, the MARPOL Convention limits the dumping of solid residues not only in port areas, but also in coastal areas. Beyond 12 miles, easily sinkable or quickly degradable materials can be dumped, while floating materials can only be dumped beyond 25 miles. The Convention limits the dumping of plastic materials on sea routes.
Residues must be stored in tightly sealed plastic bags and kept in watertight containers that are rodent-proof and easily washable.
An alternative to storing and dumping the residues in ports is the on board incinerating equipment.