There are many factors that have to be taken into consideration: From regulations and features of various oily water separation technologies, to the differences in total costs of ownership of the different systems.
To protect the seas, the International Maritime Organisation, short IMO, has ratified strict, binding provisions. They address emissions of sulphur, nitrogen and CO2 and problems with the protection of species caused by the discharge of ballast water, water pollution from chemicals, waste water and solid waste and contamination by oil.
The latter not only concerns damage caused by accidents involving tankers and similar catastrophes, but also, for example, the disposal of bilge water.
The limit for the residual oil content in bilge water from engine room bilges is set at15 ppm (parts per million) for tankers and ships with a gross tonnage of 150 tonnes when navigating outside special areas and at least 12 nautical miles from the nearest land. The prescribed maximum oil content for individual areas varies between 0 and 15 ppm.
The reasons for this can be the improper operation of oil separators on board or even a deliberate act to save on costs or time. No matter the form, the illegal disposal of oil into the sea represents a major environmental impact and is severely penalised, sometimes with fines running into the millions or bans on the ship from calling in the affected countries lasting multiple years.
Ship owners and operators must take into account the environmental requirements of the areas through which the ships in their fleet navigate and must be able to operate economically and in an environmentally sound manner when choosing the oily water separation technology.
Available products vary greatly in terms of acquisition and operating costs. In addition, some training of the ship's crew is usually necessary for operation and maintenance in order to properly operate the systems.
Gravity & filtration based systems, for example are therefore relatively straightforward to use and maintain. The advantage of these systems is the minimal effort required for start up. Annual maintenance tasks include, for example, replacement of filter cartridges and cleaning or replacement of the coalescing elements.
Gravity & filter systems are generally suitable for all types of ships. Their acquisition costs are in the comparatively low price segment and require only minimal annual costs for spare parts.
In comparison, systems based on membrane filter technology are extremely costly and also require qualified personnel in addition to high costs for spare parts. Compared to other process technologies, the amount of water that can be treated per hour in ship operation is significantly lower. However, the process using membranes is the most efficient of all conventional separation methods to date. It can achieve results of less than 1 ppm of residual oil content.
There are a number of other process technologies available, each with their unique advantages and disadvantages.
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