|The technology behind Bawat BWTS
Bawat BWTS is based on unique patented technology that represents maybe the simplest technology within ballast water treatment.
The main technology used is pasteurization. Pasteurization is a combination of heat and time and is a well-known process from the food industry.
The ballast is pumped through a pasteurizing unit, consisting of plate heat exchangers and a retention tank. When passing through the Pasteurization Unit, the BW is heated up and kept within the Retention Section for approximately 75 seconds. The heating takes place in one or two plate heat exchangers and the heat is provided by surplus heat sources – e.g. main engine jacket cooling water or exhaust heat economizers through steam or thermal oil systems.
After pasteurization, the BW passes through the regeneration section, acting as a pre-heater of the incoming ballast water, and cooler for the outgoing ballast water, taking the temperature down to 4-7 degrees higher than the inlet temperature.
When the ballast water has been treated in the pasteurizing unit it fulfills the Ballast Water Conventions outlet criteria in both USCG and IMO’s way of testing. No holding time or retreatment is necessary. There are no filters in the process, neither is use of chemicals required.
Since the water fulfills the Ballast Water Conventions outlet criteria when treatment in the pasteurizing unit is completed, it gives the opportunity to treat the water in no less than 4 different ways.
The circulation treatment
The ballast water is pumped in a circuit from just below water surface, then treated and re-introduced into the tank through jet nozzles close to the tank's bottom. When the water is led back to the ballast tank nitrogen is injected.
The injection of nitrogen in combination with the efficient pasteurizing process optimizes the total treatment time as the de-oxygenated water effectively eradicates the zooplankton and the pasteurization process reduces the phytoplankton and the bacteria concentrations to the required levels.
As an extra benefit, the de-oxygenation of the ballast water leads to substantial reductions in tank corrosion.
The ballasting in-line treatment
Since the Pasteurizing Unit is so efficient that the ballast water only needs one pass through the unit to full fill the criteria you get the opportunity to treat the water when ballasting.
The water is simply pumped from the sea to the clean ballast tank. The water is then ready for discharge anytime. No holding time or retreatment is required.
The deballasting in-line treatment
Exploiting the efficiency of the pasteurization unit, untreated ballast water can be pumped from a ballast tank through the pasteurization unit directly overboard.
The Tank-to-tank treatment
Finally, the ballast water can be treated internally when shifting the ballast water internally in the vessel. You simply pump the water from one tank to a clean tank through the pasteurization unit and then the water is treated and ready for discharge at any given time.
In voyage and alongside
Since the Bawat Ballast Water Management System is an in-voyage system as it uses the waste heat from the main engine as primary process energy, ballast water treatment takes place when the vessel is sailing.
However, if for one or another reason ballast water treatment is needed when the vessel is alongside, heat from the oil-fired boiler can be used as well.