Wastewater generated onboard ships should be treated before being released overboard into the sea. Grey and black wastewater are the two types of wastewater, and their treatment can be done independently or with the same equipment to handle both grey and black wastewater.
There are different modern forms of wastewater treatment equipment available, all of which are delivered as a complete unit ready to install in the engine room. Once upon, all wastewater was collected in a tank and pumped overboard if the ship is within a specified 12 miles from any coast, it will be pumped out to sea. To prevent pollution, international law now outlaws this practice, requiring wastewater to be treated to appropriate levels before being pushed over the edge. This read will help you to get more knowledge about wastewater treatment on ships.
Types of Wastewater in Ships
There are mainly two types of wastewater.- Grey Wastewater
- Black Wastewater
Grey Wastewater
Graywater contains wastewater from lavatory sinks, laundry, and water fountains, as well as discharges from the galley, bath, and shower. The amount of gray water produced is mostly determined by the type of ship and the number of passengers on board.Black Wastewater
The black water on a ship is gathered from toilets, urinals, and hospitals.
Blackwater and greywater are separated in different holding tanks on ships. Whether or not the effluent is treated on large ships is determined by the ship's location and destination.
Treatment of Wastewater
Treatment of Grey Wastewater
Many maritime regulating bodies require that wastewater systems treat both grey and black wastewaters. Modern wastewater treatment facilities are delivered as a single unit with all of the necessary tanks, pumps, and pipes. One of the most efficient systems uses a Membrane Bioreactor (MBR) in reverse osmosis, as explained below.
Greywater from showers, sinks, the galley, and the laundry is pumped into a wastewater tank and mixed with rotating paddles. It is then forced through a set of mesh filters to eliminate any contaminants before being piped to the sludge tank. The effluent is pumped into an aerated bio-tank, where the air is fed into the liquid via blowers to facilitate biological processes of eliminating organics.
The liquid is then poured into an osmosis tank, where reverse osmosis eliminates any solids as well as any leftover chemical molecules or viruses. This treated wastewater can then be pumped overboard without causing any environmental harm.
The osmosis process discharge is regularly checked to ensure that levels of Chemical Oxygen Demand (COD), Biochemical Oxygen Demand (BOD), Total Suspended Solids (TDS), and Ph are within current regulations. Sludge is pumped to a sludge tank from the filters and osmosis tank. Sludge can now be separated from the water and packed ready to be transported ashore or pumped ashore for disposal, depending on the treatment plant.
Treatment of Black Wastewater
By using a membrane bioreactor, the sewage can also be treated through reverse osmosis. Due to the frequent influx of liquid and solid sewage, the sewage is piped from the accommodations into a holding tank, where it is mixed. The liquor is pumped into the osmosis treatment tank through a submersible pump. Reverse osmosis is used to separate the liquids from the solids, and coliforms and other viruses are removed.
When the osmosis treatment is finished, the treated wastewater can be securely pushed overboard without hurting the environment. Instruments can track the amounts of BOD, COD, TSS, and fecal coliforms during the procedure. The sludge is transferred to a sludge tank for further processing, or it is pumped onshore when the ship is in port.
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