An introduction to ballast water treatment system(BWTS)

Definition

1. Ballast water treatment system is a device for treating the ballast water discharged from the sea. Also called ballast water management system, BWMS for short.

2. Any system in which ballast water is treated to meet or exceed the ballast water performance standards set out in Article D-2 of the International Convention on the Management and Control of Ballast Water and Its Sediments. The ballast water management system includes ballast water treatment equipment, all related control equipment, monitoring equipment and sampling facilities.

Background

Ballast is an inevitable state in ship navigation. When the ship adds ballast water, seawater organisms are also added to the ballast tanks, until the end of the voyage to the destination sea. Ballast water follows ships from place to place, causing the spread of harmful aquatic organisms and pathogens. Uncontrolled discharge of ballast water may cause harm to Marine ecosystems, socio-economic and public health. The Global Environment Fund (GEF) has listed invasive alien species caused by ship ballast water as one of the top four Marine hazards.

In order to effectively control the spread of harmful aquatic organisms and pathogens in ship ballast water, the International Maritime Organization (IMO) adopted the International Convention on the Control and Management of Ship Ballast Water and Sediment in 2004. Since 2009, the Convention has required all new ships to install ballast water treatment devices and retroactively apply them to existing ships. The Convention specifies standards for ballast water treatment, that is, the types and quantities of viable organisms in the treated water (D-2 standards).

Because no control of ship ballast water discharge to the Marine ecology, cause serious damage to public health, in 2004, the international maritime organization (IMO) by the international convention on ship’s ballast water and sediment control and management, to prevent the invasion of alien species, caused by emissions of ship ballast water caused by pathogen transmission property and resources, human health and environmental damage. The Convention stipulates that new ships must be fitted with ballast water treatment equipment from 2009 and retroactive existing vessels, and that all ocean-going vessels must be fitted with ballast water treatment equipment by 2017. Otherwise, they will not be able to enter the ports of IMO member countries after the Convention comes into force, and those who violate the Convention will face sanctions and penalties. With the coming into effect date of the “Ballast Water Convention”, all countries in the world are stepping up the research and development of ship ballast water treatment technology. Up to now, there are more than 30 foreign R&D institutions, and 13 of them have received preliminary approval from the IMO, among which Sweden, Germany, South Korea and Norway have received final approval.

China now owns a large fleet of ships accounting for 3.4% of the world’s total tonnage. China is also a big country building and repairing ships, and has a huge market of key equipment for ships. At the same time, the international market also contains huge potential.

The industrialization of ballast water treatment technology is not only an urgent need to protect the Marine ecological environment, but also of great significance to improve the loading rate of key equipment of domestic ships and the core competitiveness of shipping industry and ship building and repairing industry. At the same time, it is of great significance to the construction of naval independent equipment.

D1 standard and D2 standard

The so-called D-1 standard represents the first transitional stage in implementing the Ballast Water Management Convention. In this phase, all vessels not equipped with a compliant ballast water treatment system will be required to exchange the vessel’s ballast water using one of several approved methods in the deep sea beyond the distance specified in the Convention.

The Ballast Water Convention requires ships to discharge treated ballast water to meet the D2 standard, and the entry into force of D2 standard does not depend on the entry into force of the Convention. This is because, although the date of entry into force of the Convention is uncertain, the date of entry into force of the D2 standard in the Convention is clear for all types of ships, and the provision is retroactive, which means that it is mandatory for ships to install a ballast water management system that meets the D2 standard, regardless of whether the Convention is in force or not, whether it is a State party or not. So ships, especially newly built ships, must consider this requirement when designing ships. The current problem is that there are not enough ballast water management systems to meet the needs of all ships, so the postponement of the first effective date of D2 is inevitable. Resolution A.1005 (25) of the 25th meeting of the IMO held in 2007 addressed the issue of ships built in 2009 by postponing the date of application of the D2 standard to 31 December 2011, but the date of application of ships built in 2010 or later and existing ships will be decided by MEPC(59) held in 2009.

The next step for shipowners and ship managers is to look again at when the International Oil Pollution Prevention Certificate (IOPP) is updated for each vessel. After 8 September 2017, the International Oil Pollution Prevention Certificate will first set a deadline for each vessel to install a ballast water treatment system. This is the second phase of the Convention, where the D-2 standard specifies specific ballast water treatment options. The effectiveness OF THE BALLAST WATER treatment system is assessed on the basis of the maximum allowable amount OF viable organic MATTER in the treated ballast WATER: not more than ten viable organic matter greater than 50 microns per cubic metre of water and not more than ten viable organic matter between 10 and 50 microns per milliliter of water. The Ballast Water Management Convention also lists several indicator microorganisms and broader safety requirements. All vessels covered by the convention are required to meet D-2 standards by 2024-09-08.

All vessels in service that lack type-approved ballast water treatment systems (BWTS) must be retrofitted according to the date of IOPP certificate renewal. There are many available ballast water treatment systems, but they all have their advantages and disadvantages, and we should choose according to the specific characteristics of the vessel. At the same time, the relevant documents of vessel modification should be sent to the classification society as soon as possible for drawing approval. According to the D-2 standard, the vessel must carry the type approval certificate of the ballast water treatment system issued by an approved regulatory body, the approved technical documentation, the operation manual of the treatment system, and the International Ballast Water Management Certificate issued by the initial inspection to show that the vessel complies with the D-2 standard.

Vessels built after September 8, 2017, will be required to install ballast water treatment systems. Vessels newly built before that date, if not installed, will also need to be retrofitted accordingly within the specified time.

Existing ballast water management systems

Due to the constraints of ship space, pipeline layout and other factors, existing ships are limited in the selection of ballast water treatment technology and management system when installing ballast water management system. According to the statistical results of the number of ships that should meet D2 standard at different times, there are a certain number of ships that need to install ballast water treatment system in different time periods. Especially during the period from 2012 to 2016 when existing ships need to meet D2 standard, the number of ships installing ballast water treatment system will increase rapidly. According to the current approved ballast water treatment technology development and the present situation of the processing system, worldwide production capacity cannot meet the increasing demand, and will be installed on the ship ballast water treatment system need to be in a large shipyard completed by a large number of professional and technical personnel, then there will be a shortage of manpower and material resources.

Type of ballast water treatment systems

UV system

principle

The system uses a two-step treatment scheme to kill organic matter by filtration and ultraviolet (UV) irradiation, preventing them from reproducing.

Scope of application

In theory, UV systems can be used on any vessel, but are mainly used on vessels that do not require much ballast water and have a ballast flow of less than 1000m3/ hr.

Strengths and Weaknesses

The UV system is easy to install and modify and has few safety hazards from the classification society's point of view. It can operate at different salinities and temperatures, but its effectiveness depends on the transmittance of the water (UV-T), and the system does not work as well in more turbid water. The U.S. Coast Guard notes that all organic matter discharged from ships into U.S. waters must be in a dead state, not just in a state that can no longer reproduce. This means that a type-approved filter +UV system is more sensitive to water turbidity and requires more irradiation time to ensure organic mortality.

Electrolytic seawater system

principle

The electrolytic treatment system has a market share of about 70%, which makes it the second largest treatment system. Many of these systems use filtering for preprocessing. By feeding a current through the seawater, the system allows the salt to react with water molecules to produce a disinfectant, hypochlorite, which is then reinjected into the ballast water to kill organic matter.

Scope of application

The electrolytic system is more suitable for large vessels with large ballast water capacity, which can withstand flows of up to 8,000 m3 per hour.

Strengths and Weaknesses

In addition to accommodating large ballast water capacities, electrolyse-based treatment systems are also very effective. Its treatment of water only needs to be done when the ballast is loaded (it may need to be neutralized appropriately when the ballast is discharged). This means that the system can be sterilized on board ships, and even in ports where ballast water treatment is not available, some electrolytic systems can provide in-flight recycling. There are some drawbacks to this system, however. One of them is that the electrolytic reaction produces a small amount of hydrogen, which needs to be taken into account for safety. In addition, the electrolytic system is also very sensitive to the low salt and low temperature environment, so when needed, we should appropriately add some salt or install a heating system. Finally, electrolytic systems are more difficult to install, control and maintain than UV systems.

Chemical injection system

principle

This system is often used in conjunction with a filtration system, where chemical solutes are added to the ballast water to sterilize it. Disinfectants can be liquid or granular and usually need to be neutralized when the ballast water is discharged overboard. Some common active substances include sodium hypochlorite, peracetic acid, and chlorine dioxide.

Scope of application

Chemical injection systems are suitable for most vessels with a ballast water flow of less than 16,000 m3 per hour and are typically used on vessels with large ballast water volumes and high flow rates. The technology itself also makes it suitable for use in ballast tanks that are not often used, and it is also a good option for ships that do not need to deal with ballast water while sailing in the country.

Strengths and Weaknesses

In general, chemical injection systems have low energy requirements because their only energy requirement is to inject the chemical into the ballast water. Because only one metering pump is required as the main component of the system, the system does not take up too much space on board. This makes them easier to install than other systems. However, the chemicals used in the system, such as Peraclean and Purate, are trademarked products and will only be available at certain ports. Not only that, but chemicals need to be kept in closed containers on board, which can be a safety hazard. The use of chemicals requires stricter safety regulations and crew training. The necessary periodic chemical storage also incurs additional operating costs compared to the UV system and electrolysis system, which mainly consume electricity.

selection of ballast water treatment systems

The selection of ballast water treatment system involves a wide range of areas. On the one hand, for the specific ship, it is directly or indirectly related to the operation characteristics of the ship, the requirements of ballast water treatment, the space of the room that can be arranged for treatment equipment, the total capacity of the ballast tank, the displacement of the ballast pump, the power supply, and the coordination and operation requirements of other systems of the ship. On the other hand, as far as ballast water treatment systems are concerned, as a new product, ballast water treatment technology is under development. Although some ballast water treatment systems have been put into use, experience gained so far is limited. Each treatment system has its own characteristics. Such as using the method of electrolysis of water processing device with no processing power for water ballast water using ultraviolet devices of turbidity method of ballast water treatment ability is limited, some processing system volume is too big, and some processing system of power consumption is too large, the filtration, separation and ultraviolet method during loading and unloading, and the largest in scale choice ballast system flow rate; In contrast, chemical disinfectants and deoxidation methods are usually used to achieve a certain concentration in ballast tanks. In these systems, the effect of pump flow rate is not so much, but mainly to allow the ballast water to be kept in the tank for a long time to achieve the expected kill rate. This method may not be suitable for short voyage vessels.
For all these reasons, at present, almost no treatment system can be applied to all ships. Many treatment systems are based on a combination of two or more technologies in order to better exploit the advantages and avoid the disadvantages of various ballast water treatment technologies. In fact, the selection of ballast water treatment system is the result of comprehensive evaluation of various factors.

consideration

The following factors should be considered in the selection of ballast water treatment system:
(1) Characteristics of the ship;
(2) Characteristics of the treatment system;
(3) Layout and maintenance.

ship characteristics

1. Ship type and its ballast requirements
(1) In most cases, the type of vessel will be the determining factor in selecting the appropriate treatment system. The ballast capacity and the flow rate of the ballast pump of different types of ships vary greatly, and the total ballast capacity of ships, the amount of ballast water discharge and loading required by any port also vary greatly. Some ship types are highly dependent on ballast water, such as oil tankers and bulk carriers; Some ships have low dependence on ballast water, such as container ships. Ships WITH HIGH BALLAST DEPENDENCE USUALLY REQUIRE FULL BALLAST sailing AT NO LOAD (NO CARGO), and their ballast pumps are usually designed to pump in or out all ballast water within a certain period of time to accommodate fast port turnover times. Ships WITH LOW BALLAST DEPENDENCE, WHICH USUALLY HAVE RELATIVELY SMALL BALLAST CAPACITY and RARELY MAKE a FULL BALLAST VOYAGE (without cargo), HAVE VERY LIMITED BALLAST WATER OPERATIONS and tend TO barge, for example, from ONE TANK TO another, adjust TRIM and roll, without HAVING TO pour IN or DRAIN ALL BALLAST WATER IN a certain PERIOD of time.
(2) Some ships may include 2 or more ballast systems. For example, some oil tankers often have two ballast systems, one in the cargo area (hazardous area) and one in the engine room area (safe area); Some ships also use eductors to discharge residual ballast water. The selection of the ballast water treatment system for the dangerous area should consider the danger level of the place where it is located, usually requiring the consideration of fire and explosion protection; A ballast water treatment system requiring post-treatment may not be suitable for vessels equipped with ejectors to discharge residual ballast water.

Shipping routes

(1) The trade route of the ship is also one of the factors for selecting the processing device. At present, some countries or regions have taken unilateral actions on ballast water management that are higher than IMO standards. For ships that may berth at ports with unilateral discharge requirements, relevant requirements should be considered. For ships that do not berth in those countries or regions, there is no need to choose a higher capacity ballast water treatment system; For ships in areas with few or no special discharge requirements, ballast water management may be considered to avoid discharge or use shore facilities from an economic point of view.
(2) The effect of water turbidity, salinity and sediment content on the efficacy or maintenance of some treatment technologies. If there is a high sediment content in the water at a frequent berthing port, the influence of turbidity and sediment on the treatment system should be considered when selecting the treatment plant. If the port is often berthing at inland river ports or ports with low salinity, the influence of salinity on the treatment system should be considered when selecting the treatment equipment.
(3) The effect of sediment (silt) in the ballast tank also needs to be considered. Since the silt itself contains invasive species that can contaminate the incoming ballast water, this may result in the treatment of the ballast water as it enters or is discharged. Ballast water treatment systems that require post-treatment are usually not suitable for ships that use gravity to discharge ballast water. Treatment system features
1. The certificate requires that the ballast water treatment system should hold the necessary certificate. In accordance with Article D-3 of the Rules of the Convention, all ballast water treatment systems used for compliance with this Convention must be approved by the competent authority. Ballast water treatment systems using active substances shall also be approved by the International Maritime Organization (IMO) according to its procedures. For example, for systems using mechanical and/or physical methods (without active substances), a type approval certificate issued by the competent authority should be held; For ballast water treatment SYSTEMS using active substance technology (chemical treatment method), in addition to THE TYPE APPROVAL certificate issued by the competent authority, basic approval and final approval by IMO should be obtained.
2. Processing technology Each ballast water treatment system has its own basic characteristics which may have an impact on the particular type of vessel, route or ballast flow, and therefore on the suitability of the treatment system. The basic treatment methods and techniques can be divided into:
• Mechanical method (filtration or separation)
• Physical disinfection (UV irradiation, cavitation, deoxygenation, etc.)
• Chemical treatments (antimicrobials and agents)
Each technology has its own characteristics that can affect its suitability for a particular vessel. Most processing systems adopt a combination of the above techniques to overcome the disadvantages of a particular technique.
(1) mechanical method The system requires that the entire ballast flow be passed through a filter, spinner or other separator. In the case of high flow ballast water, the size of the equipment can be a problem. If the equipment is used when ballast water is discharged, a large amount of leachate must be retained in the vessel, which will increase the storage burden.
(2) Physical disinfection method Uv treatment is usually performed when ballast water is injected and discharged, and its effectiveness is affected by the turbidity of the water, which affects the ability of light to penetrate. Deoxygenation MAY TAKE SEVERAL DAYS TO ENSURE A KILL rate FOR aquatic organisms, and the ballast tanks must have a closed ventilation system and be completely inert.
(3) Chemical treatment The dosage should be suitable, usually within a few hours to achieve the killing rate of organisms in the water, but the ballast water discharge may still have excess drug residue, so it is usually necessary to neutralize the drug in the water to ensure that the discharge is environmentally sound. In addition, if the concentration of drugs in the ballast tank is too high, it may corrode the ballast bulkhead.
3. Size of processing system Usually, the processing capacity of the treatment system should be equal to or slightly greater than the maximum flow rate of the ballast pump, and the processing capacity of the treatment system directly determines the size of the treatment system. The shape and size of different treatment systems vary greatly, and some treatment systems require the installation of feeder lines from the ship's ballast line, which can have an impact even greater than the installation of the treatment system itself. For new ships, the layout of the treatment system can be considered in the design phase. For existing ships, the installation of the system will be a challenge due to the limited space. The spatial dimensions of different processing systems are given in Appendix 1 for reference. In addition, consideration should be given to providing suitable maintenance access to the installed treatment system, including ladders, platforms, lighting, crane tracks, lifting eyes and areas for cleaning internal components and storage and disposal of consumables, fire protection and ventilation systems as required for the premises (which may also be outside the engine room).
4. Ability of processing system Usually, when the ballast water treatment system is selected, it is necessary to ensure that it can deal with the maximum ballast water flow. However, from the perspective of reducing the cost of purchase, operation and maintenance of the ballast water treatment system, for some ships with low ballast dependence, the system with relatively small treatment capacity can be selected.
5. Handle the pressure drop of the system The installation of some ballast water treatment systems can result in a decrease in ballast water flow and pressure. For example, some automatic washing filters or spinners may lose about 10% of the indenter when removing the filter; With a treatment system that uses UV sterilization technology, the ballast water will pass through the treatment system and the back pressure will increase, which will affect the flow rate of the pump. Therefore, the operation time of the ballast will be prolonged and more power will be consumed. Therefore, when selecting the treatment system, necessary consideration should be given to the possible pressure drop during the use of the system.
6. processing system power When selecting a ballast water treatment system, the power consumption of the system should be considered, especially for existing vessels. The additional power requirement is a major constraint factor for the system selection. Some processing systems are very powerful, such as UV systems. Some existing ships will not be able to withstand the extra power consumption, and high-power equipment will also increase operating costs. Therefore, when selecting the system, the power margin of the ship's power station should be estimated in advance to confirm that the existing generating equipment can meet the additional power requirements.
7. protection grade and explosion-proof The PROTECTION CLASS (IP CLASS) AND FIRE RATING OF THE handling DEVICE and the materials used SHALL meet the requirements of the Classification Society for its installation on the ship. Special attention should be paid to the explosion-proof requirements of the equipment when the treatment system is installed in dangerous places. For example, the equipment installed in the cargo pump room must be qualified explosion-proof electrical equipment, but there is no explosion-proof grade requirement for the equipment installed in the engine room. According TO THE REQUIREMENTS OF SECTION 1.3.2.2 OF Section 4, Chapter 1, CODE FOR Classification of Steel Seaward SHIPS, China Classification Society (CCS), the ELECTRICAL equipment supporting ballast water treatment system shall have an appropriate enclosure protection type, which shall be suitable for the place of installation. For oil tanker, liquid cargo ship and other vessels carrying dangerous goods, when installing ballast water treatment devices, relevant explosion-proof requirements should be paid attention to. If installed in a dangerous area, the electrical equipment in the system should adopt the appropriate type of explosion-proof.

Layout and maintenance

On the basis of the above factors related to the ship and the treatment system, the arrangement of the treatment system on the ship and the subsequent maintenance requirements are also important factors that we must consider when selecting the ballast water treatment system. Especially for existing ships, space for handling systems can be a big challenge. Therefore, when the ballast water treatment system is selected, it should be ensured that it can be successfully installed on the ship in the future, and its subsequent maintenance should also be considered. In terms of the layout and maintenance of the treatment system, the following factors should generally be considered:
1. Ship information To assess the installation position of treatment devices on a ship, especially on an existing ship, the spatial location of equipment and systems that can be installed on the ship (e.g., engineroom layout, pump room layout, ship layout, etc.) and the configuration of the ship's ballast water system (e.g., ballast piping plan) should be known; The information shown in the diagram may directly affect the installation position of the device and the configuration requirements of the system, facilitating the smooth installation of the system.
2. Share with the existing ballast system In the system selection and arrangement of the existing ship, it should also be considered that the ballast water treatment system can share the existing ballast system as much as possible, so that the system can be well combined with the existing ballast water system, so as to simplify the refit of the system and facilitate the subsequent maintenance. 3, sampling The INSTALLATION OF SAMPLING DEVICES SHALL BE PRECONSIDERED IN THE SYSTEM LAYOUT FOR PURPOSES such AS inspection BY AUTHORIZED MANAGERS OF THE PORT STATE OR competent AUTHORITY to confirm compliance WITH the BALLAST WATER CONVENTION D2 DISCHARGE standards. The SAMPLING LOCATION AND sampling device arrangement shall comply with the relevant requirements of IMO Ballast Water Sampling Guideline (G2). 4. Control and monitoring In general, a remote control board should be set near the ballast system control board for all processing systems, or the control board can be combined in the ballast system control board. The remote control board usually includes on/off controls for the handling system, valves, and system operating status indicators. Most processing systems provide a main control panel near the equipment to facilitate off-site operation and monitoring of system performance. Shipowners may request that control, alarm and monitoring systems be combined to facilitate management. 5. Maintenance When selecting a ballast water treatment system, subsequent maintenance requirements should be taken into account. As a newly developed technology, the reliability of ballast water dispensing systems is often indicated by the complexity of the systems, such as filters, UV lamp areas, chemical delivery systems, routine maintenance of the treatment systems by the crew, and chlorine and other chemical generation systems. Usually constitute a complex processing system, its reliability will be relatively affected. The system with good reliability and low maintenance requirements can not only reduce the crew's maintenance burden, but also reduce the system maintenance cost.