Generic working details of Ballast Water Treatment System | BWTS

The BALLAST WATER MANAGEMENT-BWM Convention entered into force on 8 September 2017.

Introduction BWTS

          Presently the IMO urged the ship’s owner’s to concerning about the ballast water treatment system to avoid the marine biological Pollution caused by the conventional ballast water exchange system IMO-D1.

Hence the IMO came up with the new regulation to mitigate such violation is the ballast water treatment IMO-D2 system.

Here you can get the generic working details of ballast water treatment system (BWTS) or ballast water management system (BWMS) for your better knowledge of the operation.

IMO-D1: Ballast water exchange method

IMO-D2: Ballast Water Treatment method

IMO-D3: Approval requirements for Ballast Water Management systems

IMO-D4: Prototype Ballast Water Treatment Technologies

IMO-D5: Review of Standards by the Organization

About BWTS-Ballast Water Treatment System

          Total four types of ballast water treatment system available as of now in the market and here we will discuss the most commonly used electrolysis and UV Ballast Water Treatment Method.

1. Electrolysis method
2. UV treatment method
3. Magnetic separation method
4. Gas Treatment method 

Electrolysis method

The electrolytic method is to add or dosing the chloride/chlorine water in the ballast tank to kill the marine organism.

The electrolysis method is classified by two types

a. Side stream method

b. Full Stream method

a. Side stream method

Summary of side stream method:

It consists of the following major unit to achieve the treated ballast water for the ship’s

• Filtration unit
• Electrolyser unit
• Neutralizer unit
• TRO (Total Residual Oxidant) monitoring unit

Filtration-side stream method

          Filtration is the pre-treatment of the BWTS and the main role of this system is to filter the marine organism, sediments, and large plankton, a marine organism. It is equipped with the auto backwashing assembly to pump out the filtered particles from the filtration unit without interrupting the ballast operation and the backwash takes place automatically when differential pressure reaches the set point or the timer set value for the backwashing operation.

          

The filter size is about 50-micron candle type and it has the pressure sensor to monitor the pressure continuously in the filter chamber and followed by some control equipment’s such as a timer, relay, flow transmitter.

After completion of ballasting de-ballasting operation the filter unit used to be filled with fresh water in order to protect the filter corrosion.

Electrolyser-side stream method

          The filtered water from the main filter unit is fed to the electrolyzer unit or the dedicated filtration unit (optional) is fitted for the electrolyzer to produce the oxidant which is Sodium Hypochlorite (disinfectant) NaOCl.

Hydrogen is the by-product of the electrolyser and it’s extracted from the unit and diluted with air by the help of by gas separator and electric blower and purged into the safe atmospheric zone.

The generated Sodium hypochlorite is injected to the main ballast line and it’s reacted in the pipe with organic and inorganic species such as larva, spores, pathogens, etc.,

The sampling line from the main ballast line to TRO unit to monitor the oxidant value which should be in the range of 6.5ppm-9ppm during ballasting extracted diluted.

Electrolyser operation only during the ballasting operation

NOTE

          

The electrolyzer feedwater must be heated up through the heat exchanger if the actual temperature of the seawater falls below 15^oC to avoid the rectifier high current trips and if the ship enters the freshwater port ship should be filled up with the saltwater in the dedicated saltwater tank or aft peak tank prior to entering into the freshwater region, because the saltwater is most needed for producing the disinfectant.

Neutralizer-side stream method

          Neutralizer unit is used to neutralizing the residual oxidant (chlorite) in the treated ballast water which can’t discharge overboard directly without neutralized. That the remaining oxidant might have harmful for the marine organism in the ballast tank.

Na₂s₂o₃sodium thiosulfate is the neutralizing agent this powder agent mixed with water and stored in the form of a solution in the neutralizer tank and kept ready for injection during de-ballasting, this is called neutralization or de-chlorination.

Total Residual Oxidant (TRO)-side stream method

The TRO unit has the two types of chemical solutions in the TRO cabinet to carry out the chemical calculation of the treated water. Buffer solution and total chlorine indicators are the two types of chemicals.

Ballasting-side stream method

          TRO is used to analyze or determine the total residual oxidant concentration in the mainline during ballasting and this monitoring is carried out throughout the ballasting operation simultaneously transmits the signals to the PLC or control unit.

On the basis of the received signal from PLC, the rectifier will regulate the output current to control the generation of sodium hypochlorite solution in the electrolytic cell to maintain the required TRO value the allowed value is 6.5ppm-9ppm.

De-ballasting-side stream method

          Prior discharge/ de-ballasting the treated water should be neutralized. During de-ballasting, the sampling pump sucks the tiny amount of treated water from the de-ballasting line to TRO analyzer for analyze and determine the residual oxidant value and send the signal to the control unit. According to the received signal, the from the control unit (PLC) the neutralizer will control the injection ratio of sodium thiosulfate solution to obtain the target value which is 0.1ppm before it’s discharged.

Miscellaneous parts

          Except for this above mentioned major part in the BWTS few more parts or sensors are employed in the BWTS operation

• Rectifier used to convert the AC into DC for the electrodes in the electrolyzer
• Control cabinet or PLC panel to carry out the operation with embedded program
• Flow transmitter for various liquid flow measuring and transmitting to the PLC
• Electrolytic injection pump during ballasting operation
• Neutralizer injection pump during de-ballasting operation
• Neutralizing tank to store the sodium thiosulphate solution
• Hydrogen separator with an electric blower to separate the gas from and diluted

b. Full Stream Method-BWTS

          The full stream operation is almost same as side stream with small changes like the electrolyzer unit installed consecutively in the main ballast line instead of away in the line like side stream.

De-ballasting operation is the same as the side stream

UV TREATMENT METHOD-BWTS

Ultra Violet disinfection method consists of the following major processor parts to achieve the treated ballast water

1.   Filter Unit

2.   UV unit

3.   Monitoring and Control panel

Filter Unit-UV Treatment Method

          The filter unit is installed in the discharge side of the ballast water pump and it’s fully automatic in terms of cleaning or back-washing the filter unit without affecting the filtration process. During ballasting, the large marine micro and macro organism, larva, sediments are filtered and flushed overboard by the auto cleaning process. This pre-treated filtration unit is sophisticated and easy to operate and it has the 50-micron filter and self-cleaning assembly which is the auto cleaning unit.

Two pressure sensors are installed to measure the inlet and outlet pressure of the filter chamber and installed with the limit switch, flow transmitter, pressure gauges.

Drain valve in the filter chamber is used to drain the filter unit in case of any maintenance in the chamber. After the completion of the ballasting operation it’s recommended to fill the chamber with the freshwater in order to prevent the corrosion of the filter and the inside filer chamber due to the prolonged storage of the seawater.

UV Unit-UV Treatment Method

          The Ultra Violet system uses the high-intensity UV light to destroy the marine living organism present in the seawater after the main filter unit such as larva, bacteria, viruses, and yeasts. It has the medium pressure UV lamp the Ultraviolet lamp fitted perpendicular to the flow of water for efficient disinfection. UV unit has the stainless steel chamber and the UV emitting arc tubes fitted in it the UV arc tubes are fitted with a quartz sleeve and mounted with the chamber the quartz should have the high purity for the maximum UV transmission and followed by the electrically operated(motor) mechanical auto wiper for quartz cleaning purposes.

The seawater passes through this stainless-steel chamber via the high-intensity ultraviolet rays and the UV intensity sensor monitor the actual intensity and transmit the signal to the control unit also this the system is programmed with the ‘low UV intensity’ alarm when the UV intensity falls below the set point. A temperature sensor will shut down the system in condition of low or no water flow to avoid the overheating of the UV lamp.

In the UV disinfectant process the ultraviolet rays are emitted in the titanium dioxide plate to generate the radical to kill or sterilize the marine aquatic organism and the fungi. An atom or a molecule with an unpaired electron is known as the radicals by the radiating light of specific wavelength titanium dioxide generate the act oxygen and hydroxyl (OH), in some of the UV systems the UV rays are used to treat the water and the marine organism can be regenerated in the ballast water tank hence it should be retreated before discharging to the sea to treat the marine organism.

MONITORING and CONTROL UNIT-UV Treatment Method

          The monitoring and control unit has the full charge of the ballasting de-ballasting operation of the system and it is embedded with the PLC program with a touch screen for auto operation monitoring of the various operation of the equipment employed in the UV BWTS system.

It is performed by real-time monitoring while storing the data by the various sensor, electric ballast for the UV lamp is controlled by this unit and other associated equipment.

The control system based on the programmable logic control system is activated and de-activates the ultra violet lamp via ballast to maintain the sufficient UV dose.

OPERATION-UV Treatment Method

A. Warning up mode

B. Ballasting mode

C. De-ballasting mode

D. Bypass mode

A. Warming Up Mode-UV Treatment Method

UV lamp requires sufficient time to reach the full power which is approx. 5 min so it is necessary to start up the warm-up mode before the ballasting or de-ballasting mode for the better performance by the system.

In this case, water pumped from the sea chest and passes through the filter unit and UV chamber the treated water discharged to sea through the overboard valve instead of the ballast tank until the operator changed the ballasting mode.

Water Flow:  sea chest Ballast pump ---> Filter Unit ---> UV Chamber ---> Flow Meter ---> O/B

B. Ballasting Mode-UV Treatment Method     

During ballasting operation water pumped from the sea chest and passed through the main filter unit for the pre-treatment to filter the large planktons, larva, sediments and other marines micro-macro organism by the 50-micron candle type filter.

It is equipped with the auto back washing assembly to pump out the filtered particles from the filtration unit without interrupting the ballast operation and the backwash takes place automatically when differential pressure reaches the set point or the timer set value for the back-washing operation.In the UV chamber, the primary treatment process takes place by the high-intensity medium pressure ultraviolet and depending upon the flow rate of the ballast water, the UV lamp ballast is activated and de-activated by the PLC to maintain the sufficient UV dose to kill the marine the organism in the primary treatment. It requires the high voltage power for the medium pressure lamp inside the UV chamber, this type of UV treated BWTS is not using any kind of chemicals during ballasting except titanium dioxide-based UV treatment system which can produce the oxygen and hydroxyl (OH) chemicals for the disinfection process which have the strong disinfectant. 

Water Flow: sea chest ---> Ballast pump ---> Filter Unit ---> UV Chamber ---> Flow Meter ---> B/T

C. De-Ballasting Mode-UV Treatment Method

          During de-ballasting operation the water sucked from the ballast tank instead of the sea chest and passes through the UV chamber for the second UV dose during de-ballasting. Because after the ballasting operation the marine organism can reproduce in the ballast water tank hence it is very important that the water should retreat before discharge to the shore  Valves are lined up automatically when the de-ballasting mode operation commenced and the valves are lined up and operated by the monitoring and control unit (PLC).

Water Flow: Ballast tank ---> Ballast pump ---> UV Chamber ---> Flow Meter ---> O/B

D. By-Pass Mode-UV Treatment Method

In this mode, the system can run without the treatment cycle in case of any stoppage due to malfunction or any local regulation’s involved to avoid using the treatment system, all precautions to be taken while by-passing the ballast water treatment system and relevant persons to be duly informed.

About The Author: Mathan Kumar ETO
I am an Electrical Engineer working with Anglo-Eastern. I am from Tamilnadu and writing in my free time. Writes about my experiences and all the learnings during my work on the ship to educate my juniors and fellow friends.