TRANSMUTARE SUBSTANTIARUM BASIUM IN AURUM
Transforming Base Substances Into Gold
Ballast Water Treatment
Introduction
Ballast water may be taken on board by ships for stability and can contain thousands of aquatic or marine microbes, plants and animals, which are then carried across the globe. Untreated ballast water released at the ship’s destination could potentially introduce a new invasive marine species. Hundreds of such invasions have already taken place, sometimes with devastating consequences for the local ecosystem.
Ballast Water Treatment System
Ballast Water Treatment System (BWTS) is a system designed to remove and destroy/inactive biological organisms (zooplankton, algae, and bacteria) from ballast water. Ballast water treatment is still evolving technology with an ever-growing number of manufacturers. This means that there is limited in service experience for the systems being offered and there is a general understanding that no single system is suitable for all ship types.
Legislation
http://www.imo.org/ International Maritime Organization
IMO – the International Maritime Organization – is the United Nations specialized agency with responsibility for the safety and security of shipping and the prevention of marine and atmospheric pollution by ships.
Suppliers of BWT Equipment:
Alfa Laval
Wartsila https://www.wartsila.com/
The AQUARIUS® UV system is a two stage approach with filtration followed by disinfection using ultraviolet light. Upon uptake, seawater is first passed through an automatic backwashing filter (1st stage). The filtered seawater then passes through a UV chamber (2nd stage) where ultra-violet light is used to disinfect the water before entering the ballast tank. On discharge, water from the ballast tank is pumped through the UV chamber for a second time to complete the disinfection process prior to discharge. The filter is not used during discharge. Wärtsilä AQUARIUS® UV IMO Type Approval was awarded by the Netherlands administration during December 2012, and was followed by USCG Alternate Management System (AMS) in October 2013.
| Alfa Laval System
Processes Screens/Discs: Screens (fixed or movable) or discs are used to effectively remove suspended solid particles from the ballast water with automatic backwashing. These are extremely environmentally friendly as they do not require usage of toxic chemicals in the ballast water. Screen filtration is effective for removing suspended solid particles of larger size but is not very handy in removing particles and organisms of smaller sizes. Note: It has been noticed that though screens are highly effective in removing majority of suspended solid particles and organisms from ballast water, they alone are not sufficient to treat the ballast water according to IMO standards. Coagulation: As most of the physical filtration methods are not able to remove smaller solid particles, the method of coagulation is used prior to the filtration process to join smaller particles together to increase their size. As the size of the particles increase, the efficiency during the above mentioned filtration processes increases. Such treatment involving coagulation of smaller particles into small flocs is known as flocculation. The flocs settle more quickly and can be removed easily. Note: Some ballast water treatment systems using coagulation and flocculation utilize ancillary powder (sand, magnetite etc.) or coarse filters to produce flocs. An additional tank is required for treating ballast water for this process and thus extra space is required on board ships. Hydrocyclones: A Hydrocyclone is an effective equipment for separating suspended solids from the ballast water. High velocity centrifugal force is used to rotate the water to separate solids. As hydrocyclone doesn’t have a moving part, it is easy to install, operate and maintain on board ships. Note: It has been found that as the operation of hydrocyclone heavily depends on the mass and density of the particle, they are not successful in removing smaller organisms from the ballast water. Media Filters: Physical ballast water treatment systems with media filters can also be used in order to filter out smaller sized particles. It has been found that compressible media filters (Crumb rubber) are more suited for shipboard use because of their compact size and lower density as compared to conventional granular filtration systems. |
| This Document has been prepared by Rami E. Kremesti M.Sc., CSci, CEnv, CWEM
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