Ballast water is taken onboard or discharged into the sea by ships for stability during voyages and cargo operations. It can contain thousands of aquatic or marine microbes, plants, and animals, which can move along with the ship across the globe. Untreated ballast water released at the ship’s destination could potentially introduce a new invasive marine species. Hundreds of such invasions have already taken place, sometimes with devastating consequences for the local ecosystem.
Ships are transferring huge amount of ballast water every year and it will keep on increasing in the nearest future. As per the reports nearly 8000 to 10000 different species of microbes, marine plant and animals may be carried in ballast water every year.
For dealing with this vast growing situation, in the late 20th century the issue was raised for the first time at the IMO in 1988. After many years of complex negotiations between the IMO Member States, the International Convention for the Control and Management of Ships’ Ballast Water and Sediments (BWM) was adopted by consensus at a Diplomatic Conference held at IMO Headquarters in London on 13 February 2004.
To enter into force, the Convention required ratification by a minimum of 30 States, representing 35% of world merchant shipping tonnage, subject to which it would enter into force 12 months later. On 8th September 2016, Finland acceded to the Convention, bringing the contracting states to 52 and the combined tonnage of States to 35.14% and then it came into force from date 8th September 2017.
International Convention for the Control and Management of Ships’ Ballast Water and Sediments (BWM)
Adoption: 13 February 2004; Entry into force: 8 September 2017
The motive behind BWM convention was to prevent the spread of harmful aquatic organisms from one region to another, by establishing standards and procedures for the management and control of ships’ ballast water and sediments.
According to this convention, all ships in international traffic are required to manage their ballast water and sediments to a certain standard, according to a ship-specific ballast water management plan. All ships will also have to carry a ballast water record book and an international ballast water management certificate. The ballast water management standards will be phased in over a period of time. As an intermediate solution, ships should exchange ballast water mid-ocean. However, eventually, most ships will need to install an onboard ballast water treatment system.
A number of guidelines have been developed to facilitate the implementation of the Convention. Parties to the Convention are given the option to take additional measures which are subject to criteria set out in the Convention and to IMO guidelines
The Convention is divided into Articles; and an Annex which includes technical standards and requirements in the Regulations for the control and management of ships’ ballast water and sediments.
Ballast water management plan includes
- Introduction: objective and guidelines
- Methods of ballast water exchange
- Ballast pumps capacity and ballast water tank location, capacity and sampling points.
- Crew training and familiarization
- Duties of appointed ballast water management officer
- Ballast water reporting form and handling log.
- Explanation of need of ballast water management and reporting to the port state.
- Ship-specific Ballast water arrangements
- Crew training and familiarization by conducting meetings and video screening.
- Procedure for managing ballast water
The objective of ballast water management plan:
- Minimize risk of introducing harmful aquatic organisms and pathogens & associated sediment from ship’s ballast water.
- Awareness of risk to environment and possibility of contamination due to the discharge of ballast water.
- Training and education in management and treatment and maintenance of appropriate records.
- Safe, effective procedures for Ballast operations and facilitate environmentally safe disposal of ballast tank sediments.
- it includes guidelines to Person In charge/Chief (Operating) Officer Duties and responsibilities To ensure proper ballast water management and/or treatment procedures are followed and to maintain applicable records.
Guidelines and Precautionary Practices-
Minimize Ballast exchange in-
- Areas are known to contain potentially harmful organisms, sediment or pathogens.
- In darkness when bottom-dwelling organisms tend to rise
- In shallow waters where propellers or strong currents may stir up sediment.
- Routine cleaning of ballast tanks to remove sediments should be carried out when possible.
- Make the plan in well advance and Avoid unnecessary discharge of Ballast water in ports.
Regulation for Ballast Water Exchange, all ships using ballast water exchange should:
- whenever possible, conduct ballast water exchange at least 200 nautical miles from the nearest land and in water at least 200 metres in depth, taking into account Guidelines developed by IMO;
- in cases where the ship is unable to conduct ballast water exchange as above, this should be as far from the nearest land as possible, and in all cases at least 50 nautical miles from the nearest land and in water at least 200 metres in depth.
- When these requirements cannot be met areas may be designated where ships can conduct ballast water exchange. All ships shall remove and dispose of sediments from spaces designated to carry ballast water in accordance with the provisions of the ships’ ballast water management plan (Regulation B-4).
Methods of ballast water exchange
- Sequential Exchange Method: Ballast tanks are pumped out and refilled with clean water. When a sequential method of exchange is used, all old ballast water should be pumped out until suction is lost and then filling should be commenced.
- Flow-through Method: Ballast tanks are simultaneously filled and discharged by pumping in clean water. In this method, the tank is overflowed through air pipes. When flow through method is used, minimum three times the tank volume should be pumped through the tank.
Safety Considerations During Ballast exchange at sea
- Stability – Keep in mind free surface created during exchange operations.
- Shear forces, Bending Moments – Permissible seagoing strength limits should never be exceeded.
- Draft – Minimum, maximum drafts and associated trim condition will change.
- Weather – in areas of frequent weather changes, cyclones and in heavy icing conditions take allied precautions and avoid exchange in freezing weather conditions as air pipes and other openings may be frozen.
- Avoid over- and under-pressurization of tanks. Monitor exchange with regular soundings.
- Contingencies such as pump failure, loss of power, deteriorating weather.
- Check Domestic laws, regulations before visiting Ports
- All ballast operations to be recorded in “Ballast Operations log and details as required on Ballast reporting form for Port State Authorities.
Shipboard Ballast water treatment-Technologies proposed by industries:
Filtration Systems Filtration systems are widely used in municipal and industrial applications. Systems designs are determined by the size and type of particles to be removed. Filter systems require periodic cleaning, either manually or using automatic backflush systems.
The cost of filtration increases as smaller particles, and organisms are removed from ballast water. Since the size of filters used to treat ballast water is not likely to remove microorganisms, another treatment method would have to be used to remove microbial invaders. New technologies are developing ways to increase the flow rate through filters and prevent organisms from clogging filters, making this method of treatment more useful. For example, Use of flow-through centrifugation systems can separate particles prior to filtering and reduce filter clogging. New wedge wire filtration systems have high flow rates and are cleaned by scraping, rather than backwashing, which eliminates the need for storing and treating backwash water and thereby reduces the overall size of the filtration unit.
Oxidizing and nonoxidizing biocides. Oxidizing biocides, notably chlorine and ozone, are widely used in waste-water treatment. These chemicals act by destroying cell membranes which leads to cell death. Recent studies suggest that chlorine may not be as safe to humans as once thought. There is also a possibility that oxidizing biocides may react with seawater to form toxic chemicals. Because of these reasons, it may not be safe to release water treated with oxidizing biocides into the environment.
Nonoxidizing biocides work in a manner somewhat analogous to pesticides by interfering with reproductive, neural, or metabolic functions of organisms, such as by inhibiting respiration. The specific type of biocide must be chosen very carefully to avoid harming humans or the environment. they fall into this group of chemicals. Some of these biocides degrade into non-toxic chemicals within a few days, so if they are applied towards the beginning of a voyage they should have little effect on the environment when ballast water is released. Because of the time needed for deactivation, non-oxidizing biocides may not be the best option for shorter voyages Biocides are usually shipped and stored in the form of a concentrated solid or liquid, so they can easily be stored onboard a ship
Thermal techniques. High temperatures are commonly used to sterilize water in a wide variety of applications. It is an effective way of treatment but requires too much energy for treatment.
A study in Australia modified a ship to flush ballast tanks with heated water from the engine’s cooling system while letting ballast water overflow onto the deck then into the ocean. Ballast water reached temperatures of close to 40 C (104F) and most organisms perished. In this study, 90% of the original ballast water was washed overboard so this method is especially effective because it kills organisms with heat and also flushes the ballast tanks.
Electric pulse and pulse plasma techniques. The application of a pulsed electric field or an energy pulse to water can kill organisms. Electric pulse systems generate an electric field; pulse-plasma systems deliver a high energy pulse in water by arc mechanism and generate a plasma arc in water. The risk to the crew and the expense and size of the equipment needed to generate these pulses are the major drawbacks to this method of ballast water treatment.
Ultraviolet treatment. Treating water with ultraviolet energy to inactivate bacteria is a well-established technology. Ultraviolet radiation in the fluid at wavelengths of approximately 200 nm can destroy cellular components. This method is most effective on microorganisms and needs to be combined with another method to effectively remove all potential bio invaders from ballast water. One of the main drawbacks is that UV light is ineffective in water containing suspended matter, so ballast water may need to be filtered before treatment.
Acoustic systems. Acoustic systems use transducers to apply sound energy of specified amplitude and frequency to water to be treated. The sound energy causes cavitation, and the resulting mechanical stresses disrupt cells. Specific acoustic frequencies kill specific organisms, so acoustic treatment may be effective at removing target organisms but not the wide range of organisms found in ballast water.
Magnetic fields. Water to be treated is passed through a magnetic field of specified flux that is generated by ferromagnetic or electromagnetic devices. Magnetic forces have been shown to kill certain invertebrates, such as zebra mussels, in laboratory tests. This method is still under test on a wide variety of organisms in seawater so its effectiveness for treating ballast water is yet to be determined.
Deoxygenation. Most of the species require oxygen to survive. When oxygen is removed from the water, many organisms (but not cysts, spores, or anaerobic bacteria) are killed or usually inactive under such conditions. It is having one additional advantage of low corrosion in the ballast tank and associated pipelines due to lack of oxygen in the system. Oxygen can be removed from water by purging with an inert gas or by binding oxygen to a chemical additive.
Biological techniques. Biological techniques to control unwanted species include the introduction of additional organisms that are predators, pathogens, or competitors of the species of concern or the use of modern biotechnology methods to modify the genetics of the organism of concern.It is still under development for shipping industries use.
None of the above methods has yet been proven well to remove all organisms alone from ballast water, more research is going on for improving the proposed treatment methods, developing new methods, and determining the effectiveness of combining ballast water treatment methods
Criteria for Selecting a Treatment Method
- Safety of the crew and passengers along with
- The size, monetary cost of a treatment method and expense of the equipment
- Effectiveness at removing target organisms
- Ease of operating treatment equipment and for compliance monitoring by port authorities.
- Amount of interference with normal ship operations and travel times
- Structural integrity of the ship
One of the methods nowadays used onboard very widely is a combination of filtration unit and followed by ultraviolet disinfection unit in series. It is environmentally friendly and optimally designed solution for Ships to install and operate. This physical treatment technology effectively disinfects harmful aquatic organism and pathogen in ballast water without producing any toxic substance during ballasting and de-ballasting.
Ballast water management plant with filtration and ultraviolet disinfection unit
Filter unit –It is located in Way of the ballast pump(s) and removes larger particles and marine organisms and returns them to the local waters. When particles and organisms clog the filter screen, the unit senses differential pressure build-up and backflushing takes place automatically.
Ultraviolet disinfection unit- It is provided with high-density, medium-pressure ultraviolet (MPUV) lamps which destroy reproduction cells of living organisms in the ballast water and thereby, prevent organism reproduction and colonization. Each UV lamp is located in a quartz sleeve with water-tight seals to avoid direct water contact with the lamp. The UV chamber is equipped with UV intensity sensor to ensure required dosage of UV is applied regardless the operating condition.
CONTROL PANEL – It controls all devices and functions of the BWMS and performs real-time monitoring of operating conditions, data collection, and recording. It is provided with proportional – integral and derivative PID controls along with programmable logic controller PLC for precise control.
UV POWER SUPPLY PANEL – Used to provide power to the UV unit and other control components. It contains necessary devices to automatically adjust the power level to maintain the required UV dosage level, to protect the UV lamps and to provide safety of the power supply system.
In short, we can say that the ballast water treatment initiated during ballasting and followed by secondary treatment during deballasting. During ballasting, organisms and sediment larger than the specified size are separated by the filter and returned to local waters. Smaller organisms passing through the filter flow into the UV chamber where the UV disinfection takes place. The filter unit is normally bypassed during de-ballasting and any surviving organisms during Ballasting are treated again in the UV chamber during deballasting operation.
Many of the other treatment options are still in the experimental stage. Because installing new technologies or retrofitting ships is expensive, ship owners are reluctant to use a new technology unless it is proven effective.