Bilge Water and Ballast Water
Bilge water is the wastewater found low down in the machinery spaces of most ships and it is generated by various activities involved in keeping a ship running while at sea.
Bilge water needs to be treated with care as it can contain concentrations of various industrial fluids from the ship's machinery spaces such as coolant, lubricants, and fuel.
Ballast is water that has been taken onboard a vessel to ensure stability by maintaining a low center of gravity.
Ballast water can also contain invasive species. If a vessel takes on ballast water in foreign waters, which is then released in home waters, potentially invasive microorganisms are introduced. Invasive species have the potential to be extremely disruptive to local marine environments and can wreak untold environmental and economic damage.
Handling and Disposal of Bilge Water
Before bilge water is pumped it needs to be determined what it contains. While the price of disposing clean water is minimal, the price of disposing contaminated is extremely high in terms of environmental costs. The water must be treated before it can be released into a sewer or back into the ocean. If untreated the water is sent to a waste management facility it needs to be classified as haz-mat.
Most ships will have holding tanks for excess bilge water and "oily water treatment plants" that will do primary treatment through a centrifuge or other mechanical separation process. This process will remove most of the foreign material from the water and leave it ready to be pumped ashore.
When a ship is in harbour the process to have the bilges pumped down by shipyard staff is relatively simple. A large suction line will be fed through the ship and placed into the bilge area. On shore either a high powered vacuum pump and storage tank or a wastewater pumper truck will be used to capture the water.
Workers will monitor the line placement in the bilge(s) and move them around to ensure the suction is always drawing water.
It will be necessary to re-locate the line from time-to-time to get all the areas to a dry state.
Hoses will be removed upon completion and the bilges wiped down and/or steam cleaned if an inspection is required, or simply left in a dry condition.
Proper PPE such as gloves, coveralls, and eye protection are essential and workers should take extra care with lines and hoses to avoid contaminating other areas of the ship.
Handling and Disposal of Ballast Water
Freighters that have unloaded huge amounts of cargo will take on hundreds or thousands of tons of ballast water so they can remain low in the water for a stable journey home. This water can be pumped on, or off, the vessel and can be transferred around from tank to tank to keep the vessel in trim (that is, properly levelled and sitting in the water to maximize stability).
Ships will also take on water to compensate for fuel that is burned when the vessel is in transit.
This type of ballast water can be taken aboard and stored in holding tanks or it can even be allowed to enter the bottom of the fuel tanks to displace the fuel that is being burned. The fuel can simply float on the water or be contained in moveable membranes or bladders that move up and down in the tank. Tanks engineered in this fashion are called water compensated fuel tanks.
When ballast water is being dealt with by a shipyard, the two biggest factors to consider are:
- the volume and
- the contamination levels.
Clean ballast water from local seas can be returned into the ocean if it has not come in contact with oils or other petroleum products. If water was transferred into the fuel tanks to trim the ship and came in contact with the fuel oil, it must be treated in a centrifuge or some other mechanical device to remove the fuel oil before being discharged directly back into the sea. If the ballast water contains any animal or plant growth it must be contained and dealt with to prevent foreign or non-native species invading local waters.
Centrifuges and other shore facilities will deal with these problems once the water is pumped off the ship. Municipal approval is usually required before the water can be pumped back into the ocean.