BWMS – Selection Criteria
To install a Ballast Water Treatment System on board ship, it must be ‘type approved’ by the flag administration or a Recognised Organisation in accordance with the relevant IMO Guidelines. If the system uses an active substance, this will need to have received a final approval from the IMO before type approval can be granted.
All Ballast Water Treatment Systems have a ‘total capacity rate’ (TCR). This indicates how many cubic meters of ballast water the system can process each hour. A system with a ‘total capacity rate’ (TCR) high enough to handle ship’s ballast capacity & operational pumping rate is to be selected.
System footprints range from approximately 0.25 m2 to 145 m2, depending on their TCR. Some are single units while others can be installed as the separate components. Ballast Water treatment systems having separate components may be useful if a single space on board ship is not big enough or if the access for bringing a single system on board is difficult.
Capital and operating costs
Ballast Water Treatment System installation is a big investment & could cost as much as $2,000,000 depending on the manufacturer. As for operating costs, it depends on the type of system and starts from as little as a few dollars per 1,000 m3 of treated water. Many system suppliers quote the operating costs below $20 per 1,000 m3.
- Some systems have very high power requirements – as much as 220 kW per 1,000 m3 of treated water. Hence it is to be checked whether there will be a need to run another generator when the system is in operation or even install an additional generator set.
- Another consideration is whether a spare breaker is available in the electrical distribution board to provide power to the Ballast Water Treatment System. If not, an alternative solution has to be arranged.
Integration with existing Ballast Water System
It is advantageous to integrate the alarms and controls for the treatment system with those for the ballast pumping system, so that both can be operated from all control panels.
Type of Process Technology employed
Overview of Treatment Technologies
IMO defines ballast water treatment equipment as: “…the equipment which mechanically, physically, chemically or biologically processes either singularly or in combination to remove, render harmless or avoid the uptake or discharge of harmful organisms or pathogens. Ballast water treatment equipment may operate at the uptake or discharge of the ballast water, during the voyage, or at a combination of these events.”
Technical Challenges & System Combinations
- The treatment technologies differ in method and rate of application, scalability, holding time (required for kill rates and safe discharge), power requirements, effects on other ship systems or structure (corrosion), inherent safety and costs of operation. In many cases their efficacy varies with the conditions of ballast water, flow rates, volume of water treated & holding time. There are also issues of whether treatment is done at intake, while being held on board, at the discharge, or a combination of the three. For instance, filtration, separation & UV radiation are done during ballast. UV radiation is also used during the de-ballasting. These systems are sized for the maximum flow rate in the ballast system. Conversely chemical biocides and de-oxygenation are usually applied to attain a certain concentration in the water in the ballast tanks. .
- The efficacies of these systems do not depend so much on the flow rate of the pumps as the time the ballast is allowed to remain in the tanks to achieve the desired kill rate. Short voyages can be a problem for these technologies. .
- Matching the treatment technology to the ship type, or more accurately the ballast system type, and vessel service is the key to designing a successful ballast water treatment system. .
- To overcome the limitations of a particular technology many proposed treatment systems are based on a combination of two or more technologies. Although there are approved chemical disinfection only treatments, these are often combined with some form of the pre- treatment to make them more effective for certain vessel or ballast conditions.
Availability of consumables, spares and service support
It is important to be able to keep Ballast Water Treatment System operational at all times. If it stops working, there would be contravention of the Convention and ship could face fines or detention. Availability of spares, consumables and servicing support is to be ensured in all the areas where ship is trading.
Effect on Ballast Water Tank structure & Coatings
Corrosion and coating degeneration are two potential effects that system substances and processes may have on tanks. Hence assurance is required from the system manufacturer that tanks will not be adversely affected.
Time required for treatment to be effective
This is an important consideration depending on length of voyage and ballasting/ de- ballasting rate. For some Ballast Water Treatment plants, 24 hours of storing of ballast water in the ballast tanks after treatment can ensure effective disinfection to the Regulation D-2 and no re-growth of organisms were found in the treated water after 10 days. Extent of reduction in the vessel’s ballasting rate following installation of the treatment system also needs to be considered i.e. detail of the pressure drop.
Health and Safety aspects for Crew
A number of different chemicals or chemical processes are employed in the ballast water treatment systems available, which are as follows:
- chlorine dioxide
- peracetic acid
- hydrogen peroxide
- menadine/vitamin K
- perchloric acid.
Some systems generate chemicals during the treatment process; for others, chemicals are required to be stored on board.
If chemicals are stored on board, the crew will require training on their use and handling. Suitable storage space for the chemicals & proper ventilation are of paramount importance. The Safety Data Sheets for chemicals to be stored on board need to be consulted & where necessary the appropriate fire protection & extinction arrangements will need to be installed.
In the case of systems that generate chemicals during the treatment process, the crew will require training on the hazards associated with them. Advice on the storage and handling of chemicals is contained in the IMO Circular: BWM.2/Circ.20.
Ease of maintenance, calibration and water sampling
It needs to be ensured from suppliers that maintenance of Ballast Water Treatment plant, calibration of monitoring and measurement equipment and sampling of ballast water is easy.
Provision of Emergency bypass operation
To assure the ballast water management system (BWMS) remains operational in the event of the treatment system failing, suitable by-passes or overrides are to be installed to protect the safety of the ship and personnel.
The by-pass is to activate an alarm, and the by-pass event should be recorded by the control equipment.
If ship is a tanker or gas carrier, and the system is going to be installed in a ‘gas dangerous area’ (i.e., in the cargo area), then system must be certified ‘gas safe’.