Sewage Treatment Plant on Ships
Discarding sewage produced onboard on a ship is one of the few tasks on a ship which should be taken utmost care of if one wants to save him and his shipping company from heavy fine. The sewage generated on the ship cannot be stored on the ship for a very long time and it, for this the reason, it has to be discharged into the sea.
Though sewage can be discharged into the sea, we cannot discharge it directly overboard as there are some regulations regarding discharging of sewage that needs to be followed. Sewage on the sea is generally the waste produced from toilets, urinals, and WC scuppers. The rules say that the sewage can be discharged into the seawater only after it is treated and the distance of the ship is 4 nautical miles from the nearest
But if the sewage is not treated this can be discharged 12 nautical miles away from the nearest land. Also, the discharged sewage should not produce any visible floating solids nor should it cause any discolouration of the surrounding water. The details of the sewage discharge regulations can be found in MARPOL Annex IV.
The most preferred type of sewage treatment plant is that involving
aerobic bacteria. The Anaerobic bacteria are equally capable of
decomposing and breaking down the sludge but during the process,
they generate and release harmful gases such as H2S and methane
which are toxic and dangerous for aquatic organism.
Waste Oil Incinerator
• According to Annex VI of MARPOL 1973/78 Convention of IMO for prevention of air pollution from ships, the guidelines regarding the waste material storage and disposal of waste at sea need to be strictly followed. Incineration of various materials such as galley waste, food scraps, accommodation waste, linen, cardboard, oil sludge from lubricating oil, fuel oil, bilge and purifier, and sewage sludge, is one of the most effective ways of disposal and saving storage capacity of the tanks and waste storage containments on ships. Moreover, the residue left from the incineration can be easily disposed of off as it mainly consists of ash.
What not to incinerate
• The following material not to be incinerated:• Annexe I, II and III cargo residues of the present Convention and related contaminated packing materials;• Polychlorinated biphenyls (PCBs).
• Garbage, as defined in Annex V of the present Convention, containing more than traces of heavy metals; and refined petroleum products containing halogen compounds
• Incineration of sewage sludge and sludge oil generated during the normal.operation of a ship may also take place in the main or auxiliary power plant or boilers, but in those cases, shall not take place inside ports, harbours and estuaries.
• COMMUTATOR refers to the device in Collection, Holding & Transfer System holding tanks that smash the clumps in collected human waste to a more liquid form, so that it won’t clog the overboard discharge pipes.