1. Disposal of sewage and liquid wastes

Ships are not generally permitted to discharge sewage or any other liquid containing contaminating or toxic wastes within an area from which a water supply is drawn or in any area restricted for the discharge of wastes by any national or local authority. Overboard discharge in harbours, ports and coastal waters is subject to the regulations of the governing authorities in these areas. Sewage, food particles, putrescible matter and toxic substances must not be discharged to the bilge.

Any country may provide special barges for the receipt of these wastes or shore connections that input to the sewer system. Where the shore servicing area or barge does not provide a hose or connections to receive these wastes, the ship must provide a special hose and connections large enough to allow rapid discharge of wastes. This hose must be durable and impervious, have a smooth interior surface, be of a size different from that of the potable water hose or other water-filling hoses and be labelled “FOR WASTE DISCHARGE ONLY”. After use, the hose must be cleaned by thorough flushing with clear water and stored in a convenient place labelled “WASTE DISCHARGE HOSE”.

The prohibition against discharge of wastes near a water supply intake or in any body of water where measures for the prevention and control of pollution are in force will require the provision of retention tanks or sewage-treatment equipment on board.

Systems need to be designed and constructed so as not to leak wastes and need to be amenable to ready inspection to check for leaks or bursts. Approved backflow preventers (vacuum breakers) or acceptable air gaps must be installed in the water supply lines to the grinders. All piping should be colour coded and labelled (e.g. according to ISO 14726:2006) at least every 5 m to avoid confusion and possible cross-connection to potable water. Drain, soil and waste pipes need to be maintained frequently to prevent clogging and the backflow of sewage, greywater or contaminated wastes into the fixtures and spaces served by the collection system.

2. Grease traps

All galley wastes, exclusive of ground refuse, that may contain grease must be made to flow through grease interceptors (grease traps) to a retaining box before discharge or treatment on board ship. The design of the interceptors may need to be approved by the appropriate authority of the country of registration. The grease collected may be disposed of by incineration, by storage for shore disposal or by overboard discharge on the high seas. Overboard discharge may occur after a suitable separation distance with the closest line of land, such as 3 nautical miles (12 nautical miles in territorial sea), in compliance with other national rules.

3. Treatment

All ships must be equipped with facilities for managing wastes from toilets and urinals, hospital facilities and medical-care areas, and food refuse grinders. These facilities include treatment systems and/or safe holding tanks, properly equipped with pumps and piping. Wastes from safe holding tanks may be discharged to port connections or to special barges or trucks. The design of treatment systems and waste-holding tanks needs to be based on a suitable volume (e.g. 114 litres of liquid waste per capita per day) and may need to be approved by the appropriate authority of the country of registration.

For ships where the normal wastewater flow to be treated is quite large, exceeding 4750 litres per day, treatment must be designed to produce effluent of a suitable quality, such as biochemical oxygen demand of 50 mg/l or less, a suspended solids content of 150 mg/l or less and a coliform count of 1000 or less per 100 ml.

Excess sludge must be stored for appropriate disposal to land-based facilities or when on the high seas. For ships with a daily flow of wastewater to be treated that is quite small, less than 4750 litres, treatment may be limited to passing the wastes through grinders, followed by disinfection to produce an effluent with a coliform count of 1000 or less per 100 ml.

Chlorination, or an equally effective method of disinfection, may need to be installed, as recommended by the manufacturer, to produce an effluent meeting the coliform requirements set by the relevant authorities.

1. Facilities for waste storage

To prevent corrosion, the interiors of food and garbage lifts may need to be constructed of stainless steel and meet the same standards required for the storage, preparation and service of food. Decks need to be constructed of a durable, non-absorbent, non-corroding material and have a suitable internal cove, at least 10 mm along all sides. Bulkhead-mounted air vents must be positioned in the upper portion of the panels or in the deckhead. To help with cleaning and removal of spills, a drain at the bottom of all lift shafts must be provided, including the provision of platform lifts and dumbwaiters.

If used to transport waste, the interiors of dumbwaiters must be readily cleanable and constructed of stainless steel or similar and meet the same standards as other food service areas. The bottom of the dumbwaiter should include a suitable cover.

Garbage chutes, if installed, need to be constructed of stainless steel or similar and have an automatic cleaning system.

In waste-management equipment wash rooms, bulkheads, deckheads and decks need to be constructed to meet the same standards required for the storage, preparation and service of food. A bulkhead-mounted pressure washing system could be provided with a deck sink and drain. An enclosed automatic equipment washing machine or room may be used in place of the pressure washing system and deck sink. Adequate ventilation is required for extraction of steam and heat.

The garbage storage room should be well ventilated, and the temperature and humidity controlled. A sealed, refrigerated space must be used for storing wet garbage. The space needs to meet the same criteria for cold storage facilities for food. The room must be of adequate size to hold unprocessed waste for the longest expected period when off-loading of waste is not possible and must be separated from all food preparation and storage areas.

In all the garbage holding and processing facilities, there need to be easily accessible hand-washing stations with potable hot and cold water, hose connections and a sufficient number of deck drains to prevent any pooling of water. The sorting tables in garbage processing areas must be constructed from stainless steel or similar and have coved corners and rounded edges. Deck coaming, if provided, needs to be adequate, at least 8 cm, and coved. If the tables have drains, they should be directed to the deck drain, which requires a strainer. A storage locker must be provided for cleaning materials to keep them away from foods. Adequate lighting, at least 220 lux, is required at work-surface levels, and light fixtures need to be recessed or fitted with stainless-steel or similar guards to prevent breakage.

To facilitate storage, tops and bottoms must be removed from all empty metal containers or containers with metal ends, and the remaining parts flattened. Containers of paper, wood, plastic and similar materials should also be flattened for convenient space-saving storage. Dry refuse must be stored in tightly covered bins or in closed compartments, protected against weather, wash and the entry of rodents and vermin. The containers must be thoroughly cleaned after emptying and treated with insecticides or pesticides, if necessary, to discourage harbourage of rodents and vermin.

2. Excess sludge

Excess sludge is typically stored appropriately for appropriate disposal to land-based facilities or when on the high seas.