There are several types of ballast water treatment systems (BWTS) available on the market or currently in development. They work on the principles of one or a combination of mechanical, physical and chemical.
Most ballast water treatment systems use a two-step process, usually mechanical filtration followed by disinfection.
Common methods include:
On intake the ballast water is filtered before passing through disinfection unit, typically chemical injection, electro- chlorination or UV.
Upon discharge, the filter is bypassed and, depending on type, the ballast water will be pumped directly overboard. Chemical and electro-chlorination systems cannot provide secondary treatment (i.e. disinfection at discharge).
At present, the only system that has the ability to disinfect during deballasting is ultraviolet. This is because UV is the only technology that has an instant disinfection effect and does not generate harmful residual substances in the seawater when discharging overboard.
IMO defines an ‘active substance’ as “a substance or organism, including a virus or a fungus, that has a general or specific action on or against harmful aquatic organisms and pathogens”
The Electrocatalysis Unit is able to produce large numbers of hydroxyl radicals and other highly active oxidizing substances to kill all organisms in ballast water within several nanoseconds. The whole sterilization process is completed inside the EUT Unit. During the treatment process, the Ultrasound Unit can clean the surface of Electrocatalysis Unit regularly to keep the long-term treatment effectiveness of the electrocatalysis material.
The Unitor treatment system employs a combination of cavitation, chemical treatment, and filtration to remove or inactivate organisms in the ballast stream. Ballast water is treated on uptake only. During uptake water is drawn through an in-line reactor vessel installed on the suction side of the ballast pump. The reactor houses both the cavitation and chemical treatment processes. A 40 micron filter downstream of the ballast pump separates organisms and sediments which are back-flushed overboard at the uptake source.The cavitation process creates shear forces in the fluid which rupture the cell walls of entrained organisms. Chemical treatment is achieved with sodium hypochlorite (produced via electro-chlorination) and ozone (produced via separately mounted generator). These agents are injected into the reactor at low concentrations (< 1.0 ppm) and are neutralized almost.
immediately after injection. Chemical neutralization is not required.
Power is continuously supplied to both the hypochlorite and ozone generators. If the vessel operates in fresh water, the fall-off in hypochlorite generation is compensated for by the continued generation of ozone. A vessel operating in fresh water will rely primarily on the production of O3 for disinfection with only minimal amounts of hypochlorite being generated.
The UV lamps emits short wave radiation into the water. This will expose any organisms or pathogens with a high dose of UV light. The UV-exposure will kill or inactivate the remainder of plankton as well as any bacteria/viruses.
Filtration: during ballasting, total volume of ballast water flow through a 50um filtration unit, marine organism and particles larger than 50um are filtrated and discharged back to local water;
Seawater Electro-chlorination for disinfection: a small amount of filtrated sea water flows into electrolysis unit to generate high concentrated Sodium Hypochlorite solution, which will be injected back to main ballast pipe line after de-gas treatment.
Sodium Hypochlorite solution will be mixed with the sea water form main ballast pipe line to a certain designed concentration, which is able to kill the marine organism including spores, lavas and pathogen within the water, in order to meet the disinfection standard (D-2 Standard and the others). The concentration of active agent in main pipe line is monitored and controlled through TRO unit and system main control unit.