At ballasting the ballast water treatment process performs two main unit operations: mechanical separation (filtering) and disinfection (electrolysis based chlorination). In the first step, the filters (50 μm filter fineness) remove particles, sediments and organisms of the larger size class. This allows the following disinfection step to minimize the use of NaOCl, a chlorine compound. In the second step, the sodium hypochlorite solution generated from the electrolysis unit is injected into the filtered influent ballast water to effectively disinfect organisms of the smaller size class and bacteria remaining in the filtrate. At de-ballasting, neutralization unit decreases the total residual oxidants (TRO) concentration if required before the ballast water discharge.
A Back-flushing Filter is installed on ballast pump discharge line and it will filter
organisms and particle materials over than 50 micrometers. There is back-flushing line on Back-flushing Filter for cleaning itself. Usually Back-flushing Filter is combined with one(1) set of Back-flushing Pump which supplies clean seawater for cleaning. A Back-flushing Valve is installed on Back-flushing Filter discharge line and it makes more pressure on Back flushing Filter to help back-flushing operation. Back-flushing Pump and Back flushing Valve are installed on back-flushing line for pumping out back-flushing water overboard.
After this filtering process, second disinfection process of generating and injecting biocide(Sodium hypochlorite, NaOCl) are as follows. Electrolysis unit electrolyzes seawater that is coming from the separate branch line from main ballast line. Only 0.5% of total ballast water flow is used for producing disinfectant solution. Booster Pump is installed on this line to pumping the clean seawater to Electrolysis Unit. Seawater should be met that temperature over than 5℃ and salinity over than 10 PSU. If seawater does not meet these conditions, A Heat Exchanger will be used.
High salinity seawater shall be loaded in the separated seawater tank (sometimes also called technical sea water tank ) in advance and it will be used when the vessel goes to the brackish water zone. Temperature sensor and salinity sensor give alarm to the crew. And after, seawater flows into the Electrolyzer , Seawater is electrolyzed in the Electrode. The concentration of generating biocide in Electrode is decided by current control of Rectifier. When the seawater electrolyzed, hydrogen gas, oxygen gas and chlorine gas are generated as byproduct. These gases are
separated in the hydrocyclone and vented out safely after diluted by blower. There is gas monitoring system on vent line. When the biocide solution injected to main ballast line, injection rate is controlled by Flowmeter and Flow Control Valve.
After injecting to the main ballast line, final concentration of TRO is checked by TRO
sensor and the data transmitted to MCP for current control.
Flowmeters on main ballast line checks flow rate of ballast water.
After Peak Tank is located in the aft of the vessel and it is separated with main ballast system. So, BWMS system is designed to treat the seawater separately of those two ballast system
Bypass mode is operated only in emergency case. In this mode, seawater flows into the ballast tank directly without any treatment. This operation shall be recorded in the system.
For deballasting operation TRO CONCENTRATION > 0.1ppm always and zero for USCG mode.For Ballasting operation TRO value has a range and is not than 7ppm.
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