the conventions for preventing marine pollution caused by ships mainly include MARPOL 73/78, which aims at marine oil substances, toxic liquid substances, harmful substances in packaging, domestic sewage, marine garbage and atmospheric pollutants discharged by ships. The convention has been applied to ships that account for 99% of the world's total merchant tonnage. In addition to MARPOL 73/78, there are anti-fouling paints for harmful ships under the International Convention for the Control of Harmful Anti-fouling Systems on Ships in 2111 (hereinafter referred to as the Anti-fouling Convention), ballast water for ships carrying exotic organisms and pathogens under the International Convention for the Control and Management of Ballast Water and Its Sediments in 2114 (hereinafter referred to as the Ballast Water Convention), and the Hong Kong International Convention for the Safe and Environmentally Sound Recycling of Ships in 2119 (hereinafter referred to as the Ship Recycling Convention) In the relevant conventions on preventing marine pollution from ships, science and technology, as the technical support for the formulation and implementation of the conventions, make the technical standards in the conventions clear and feasible; The formulation and revision of the convention provide opportunities and impetus for the development of science and technology. First of all, the achievements of science and technology are adopted by the shipping industry, which promotes the technical progress of the shipping industry and becomes a strong technical basis for formulating and amending the convention. Without science and technology, it is difficult to control ship pollution. For example, the convention on anti-fouling bottom is formulated to limit the use of anti-fouling paints that are harmful to the environment, but to prohibit the use of anti-fouling paints containing TBT, alternative measures must be taken first; The requirements for cargo hold residues in Annex II of MARPOL 73/78, which came into effect in 2117, are much lower than the original provisions, which can only be realized on the basis of improving the technical performance of pumping equipment and piping arrangement; MARPOL 73/78 Annex VI requires the gradual reduction of sulfur content in fuel according to the technical development of marine fuel. Sometimes, the formulation of international maritime conventions is ahead of technological development. For example, when the ballast water convention was formulated in 2114 and ships were required to install ballast water management systems, there was no mature ballast water treatment technology and commercial equipment available to ships internationally. After the introduction of the ballast water convention, the international community quickly invested manpower and material resources in research and development, and devoted itself to solving the threat of invasion by alien organisms and pathogens. Up to now, many manufacturers have introduced the ballast water management system approved by the type, and IMO thinks that it can basically meet the needs of ships suitable for the year 2111. When formulating and putting forward relevant technical requirements for pollution prevention conventions, IMO not only relies on its own technical strength, but also relies on the United Nations Group of Scientific Experts on Marine Pollution (GESAMP) to solve technical problems in formulating and reviewing conventions and implementing them. For example, GESAMP-BWWG Joint Technical Group is responsible for reviewing the technical problems of using the active substance ballast water management system and making recommendations for approval/disapproval to the Committee; GESAMP- EHS joint technical group is responsible for the assessment of the hazards of hazardous substances in shipping. 2 Basic Principles of Convention and Technology for Preventing Pollution from Ships There are two ways for ships to produce pollutants: operational pollution caused by normal operation of ships; Accidental pollution caused by various accidents of ships. There is also the pollution caused by dismantling when the ship is retired. Operational pollution of ships means that ships will produce some pollutants in normal operation, some of which are caused by cargo residues, such as washing water and ballast water in cargo holds of oil tankers and chemical tankers; Part of it is produced by the ship itself, such as oily sewage in the engine room, oil residue of fuel oil, domestic sewage, ship garbage and atmospheric pollutants produced by the ship; The transfer of exotic aquatic organisms and pathogens caused by operating in different waters and using ballast water as the medium; The use of antifouling paint containing organic tin causes damage to the marine environment. Accidental pollution of ships refers to accidents such as collision, grounding, hitting rocks, fire and explosion, as well as accidents such as damage to loading and unloading equipment and human factors, which will cause a large number of pollutants to be discharged in a short time, thus causing major or even catastrophic pollution damage to local sea areas. The basic principles of the convention for the prevention of pollution from ships are: reducing the generation of pollutants on board; Control the discharge of pollutants from ships; Minimize the impact on the marine environment after pollutant discharge and limit the accidental discharge of pollutants from ships to the maximum extent. 2.1 Reduce the generation of pollutants on board. Obviously, it is an effective way to reduce the pollution from ships by keeping pollutants off board or reducing the amount of pollutants generated on board. Some provisions in the Convention for the Prevention of Pollution from Ships are put forward to reduce the generation of pollutants. For example, Annex I of MARPOL73/78 stipulates that crude oil tankers with a deadweight of more than 21,111 tons should be equipped with special ballast tanks in order to reduce the generation of oily sewage from ships; MARPOL73/78 Annex II Rules for Controlling Pollution of Bulk Toxic Liquid Substances In order to reduce the residues in cargo holds, technical measures such as compulsory pre-washing, effective cabin sweeping and ventilation procedures were put forward. Annex VI of MARPOL73/78 stipulates that controlled ozone depleting substances are not allowed to be used on board, and the emission limit of NOx for diesel engines installed on board after 2111; The anti-fouling convention stipulates that ships cannot apply anti-fouling paint containing TBT; Annex 1 of the Ship Scrapping Convention lists the list of hazardous materials whose use is prohibited or restricted, and stipulates that ships should try to reduce cargo residues, residual oil and other pollutants before dismantling. 2.2 Controlling the discharge of pollutants from ships In the case that pollutants will inevitably be produced, the technical measures to reduce the pollution caused by ships include: treating the pollutants produced on board the ship or discharging the pollutants to shore receiving facilities. For example, Annex I of MARPOL 73/78 stipulates that engine room sewage must be treated by 15ppm oil-water separation equipment before it can be discharged, and oily sewage from cargo hold must be discharged through oil discharge monitoring system; Annex IV of MARPOL 73/78 requires ships to be equipped with domestic sewage treatment devices and domestic sewage crushing and disinfection systems; Annex VI of MARPOL 73/78 stipulates that the requirement of replacing 1.5% m/m fuel in SOx control area is to install exhaust gas filtration system to reduce SOx emission below the allowable value; Ballast water convention requires ships to install ballast water treatment system to remove exotic organisms and pathogens carried in ballast water. Another effective technical measure to reduce the discharge of pollutants is to discharge the pollutants produced on board to the shore receiving facilities. In this case, there is a need for receiving facilities because the convention completely prohibits the discharge of highly toxic or environmentally degradable substances, such as: any plastic products are prohibited from entering the sea; It is forbidden to use antifouling paint containing TBT; Class X toxic liquid substances are prohibited from being discharged. In other cases, it is mainly limited by processing technology. Some processing technologies are easy to realize on shore, but they are difficult on board. For example, Annex I of MARPOL73/78 stipulates that the residues of ship bilges and sludge tanks can be discharged to shore receiving facilities for treatment through standard discharge joints; Annex II of MARPOL 73/78 stipulates that the sewage containing chemicals produced by compulsory pre-washing shall be discharged to shore receiving facilities; In addition, Annex IV, V and VI of MARPOL 73/78 all require onshore receiving facilities; Ballast water convention requires that ship repairing and cleaning ports should be equipped with ballast tank sediment receiving facilities. 2.3 Minimize the impact on the marine environment after pollutants are discharged. At the current level of science and technology, ships will inevitably produce and discharge some pollutants in the course of operation, which is why the pollution prevention convention does not require all pollutants to be "zero-discharged". Of course, such emissions are within the scope of "environmental capacity". For example: oily sewage with oil content within 1.5 ppm; Sewage containing a certain concentration of toxic liquid substances; Some kinds of ship garbage; NOx and SOx gases below a certain limit. In order to ensure that the pollutants allowed to be discharged can be mixed with seawater as soon as possible without obvious impact on the environment, the convention also stipulates corresponding discharge conditions, such as: discharge of oily sewage below 1.5 ppm on the waterline; The sewage containing toxic liquid substances allowed to be discharged must meet the conditions of underwater discharge, self-propelled ship speed of 7 knots, non-self-propelled ship speed of 4 knots, distance of 12 nautical miles from the nearest land, water depth of 25 meters, etc. The conditions for domestic sewage to be allowed to be discharged are that it is 3 nautical miles away from the nearest land, the discharge is crushed and disinfected, the speed of the ship is more than 4 knots, and it is discharged at a medium rate. In order to protect the more sensitive sea areas, the Convention stipulates more stringent pollutant discharge standards for "special areas", "particularly sensitive sea areas" and "SOx emission control areas". For example, when an oil tanker is in a special area, it is forbidden to discharge oil or oily mixture from the cargo oil area on board into the sea; The Antarctic region is a special region in Annex II of MARPOL 73/78, and it is forbidden to discharge any toxic liquid substances or mixtures containing such substances into Antarctic waters. As SO emission control areas in the Baltic Sea and the North Sea, the sulfur content of fuel should be limited to 1.5% m/m or the total amount of SOx emission from ships including main and auxiliary propellers should be reduced to 6.1g /kW·h or less. 2.4 To control the accidental discharge of pollutants from ships to the maximum extent is the main risk of local major pollution damage. Previous major oil spill accidents have caused long-term ecological damage or disasters in some sea areas. In order to prevent such accidents, Annex I of MARPOL 73/78 puts forward targeted technical measures. For example, in order to limit the oil spill after a single oil tank is damaged, the tank capacity of a single oil tank is limited: the maximum tank capacity of each oil tank of any oil tanker shall not exceed 41111m3；; In addition to the capacity requirements, the special ballast tanks for oil tankers are also required to be arranged in the most vulnerable parts of the ship to provide a protective measure to prevent oil from flowing out in the event of grounding or collision. In view of a number of major oil spill accidents of single-hull tankers, Annex I of MARPOL 73/78 adds the requirements of double-hull for tankers delivered after 1996 and tankers delivered before 1996. In order to provide appropriate protection against oil pollution in collision or grounding accidents, Annex I of MARPOL 73/78 stipulates that oil tankers delivered on or after October 1, 2111 should be designed to ensure that the oil spill in accidents is within a certain limit; In addition, for each oil tanker with a gross tonnage of 1.51 tons or more and each non-oil tanker with a gross tonnage of 411 tons or more, it is required to have an Emergency Plan for Oil Pollution on Board approved by the competent authority to ensure that correct and effective methods are adopted in the emergency of pollution accidents. 3 The development trend of new technologies to prevent ship pollution With the improvement of people's environmental awareness, more and more further development is needed in terms of legislation, technology and management. Under the promotion of IMO Convention, the shipping industry has also adopted more new technologies to prevent ship pollution, which play a great role in better protecting the marine environment.