How to deal with the damage caused by oil spill to seawater

According to the conventional oil spill treatment measures, the traditional treatment method is taken immediately after the oil spill accident, and it is also the most commonly used method to deal with oil spill accidents. According to the different equipment used, it is divided into three categories. From the point of view of physical treatment methods, physical treatment methods mainly contain and recover the residual oil on the sea surface, which is closely coordinated with other treatment methods such as combustion method, oil absorption material, oil dispersant decomposition, biodegradation and so on. The treatment efficiency is greatly affected by weather, sea conditions and oil spill types. There are several physical treatment methods actually used in oil spill accident treatment: (1) purse seine method: after the oil spill reaches the sea surface, purse seine should be carried out first to prevent it from spreading on the sea surface, and then try to recover it. The fence should have the properties of strong oil retention, good wave retention, strong wind and wave resistance, convenient use, toughness and durability, easy maintenance and difficult attachment to marine life. The fence can not only prevent the oil spill from spreading horizontally, but also prevent the crude oil from condensing into tar balls and spreading vertically on the sea surface, that is, drifting with the flow. Fences can be divided into four categories: curtain fences: mainly used under the conditions of calm sea surface and good coastal conditions; Hedging fence: mainly used in sea areas with high velocity; Sealed fence: used in periodic tidal waters; Fire fence: used in combination with incineration technology. (ii) Oil recovery vessels: Oil recovery vessels recover oil without changing its physical and chemical characteristics. At present, there are the following types of skimmers widely used: suction skimmers: the main types are vacuum skimmers, wedge skimmers and turbine skimmers. Adsorption skimmer: The main types are belt skimmer, drum skimmer, brush skimmer, disc skimmer and mop skimmer. Heavy oil skimmer: The operation method is the same as the general skimmer, but the heavy oil skimmer is used to remove the mixture of high viscosity oil and emulsified oil and water. (3) Oil-absorbing material: lipophilic oil-absorbing material can make spilled oil adhere to its surface and be absorbed and recovered. Oil-absorbing materials are mainly used in coastal and port waters to deal with small-scale oil spill accidents. There are three kinds of raw materials for making oil-absorbing materials: polymer materials: polyethylene, polypropylene, vinegar and so on. Inorganic materials: diatomite, perlite, pumice, bentonite; Fiber: straw, wheat straw, sawdust, grass ash, reed, etc. According to II, the main feature of chemical treatment method is to change the physical and chemical properties of oil, which can be directly applied to oil spill treatment or used as the follow-up treatment of physical treatment method. Chemical treatment methods include the following: (1) dispersant: oil spill dispersant is a uniform transparent liquid composed of surfactant, penetrant, cosolvent and solvent. Dispersants can reduce the surface tension between oil and water, emulsify spilled oil on the water surface to form emulsion, disperse oil into tiny oil beads dispersed in water, and make spilled oil particles easily react with chemicals in seawater, easily degraded by microorganisms that can degrade petroleum hydrocarbons, and finally converted into water-soluble substances such as CO2, which accelerates the process of oil purification by the ocean. The general dosage of dispersant is 1% ~ 20% of the oil spill. Easy to use, the effect is not affected by weather and seawater conditions. It is the first choice to deal with oil spill under harsh conditions. At present, dispersant is widely used to deal with conventional oil spill accidents in China, but it may destroy the ecological environment in the process of use. The main dispersants used in the world today are: traditional dispersants; Concentrated anhydrous dispersant; Concentrated water dispersant. (2) Coagulant: It can solidify petroleum gum into a viscous or hard gel. Its advantages are low toxicity, unaffected by wind and waves, and effective prevention of oil diffusion. The development and application of coagulants have attracted the attention of many countries, and a large number of patent papers have been published in recent years. (3) Other chemicals: demulsifier used to destroy oil-water mixture; Bioremediation compounds that accelerate the biodegradation of petroleum: In addition, there are combustible materials and viscous additives. According to natural degradation, people do not take any action, and oil is naturally purified by the ocean. 2. Emerging oil spill treatment methods Generally speaking, these methods are only used as follow-up treatment methods of other methods or are still in the experimental research stage. 2. Bioremediation technology believes that some microorganisms naturally existing in the ocean or soil have strong ability to oxidize and decompose oil, and this characteristic of microorganisms can be used to clean up oil spills at sea. Biological treatment will not cause secondary pollution, and can be used in combination with other additives that can accelerate biological natural degradation. Compared with chemical and physical methods, bioremediation has little impact on people and environment, and the cost of bioremediation is only 30% ~ 50% of that of traditional physical and chemical remediation. The natural biodegradation process of petroleum is slow, and various measures can be taken to strengthen this process. The commonly used technologies are: first, adding surfactants to promote the utilization of petroleum hydrocarbons by microorganisms; Second, provide the conditions needed for the growth and reproduction of microorganisms (provide O 2 or other electron receptors and apply nutrition); Third, adding microorganisms that can degrade petroleum pollutants efficiently. At present, it seems that the bioremediation of oil-polluted beaches is mainly based on the application of nutrition, lacking the intersection and integration with other technologies. At the same time, because bioremediation is a complex heterogeneous system, involving knowledge of microbiology, engineering, ecology, geology, chemistry and other disciplines, its mechanism of action is still unclear. 2.2. The combustion method requires the use of various combustion improvers, so that a large amount of spilled oil can be burned in a short time, without complicated equipment, and the treatment cost is low. However, considering the influence of combustion products on the growth and reproduction of marine life, it may cause damage to nearby ships and coastal facilities, and the smoke generated during combustion will also pollute the atmosphere. Generally, the treatment object is large-scale oil spill and oil pollution in the Arctic Ocean waters, and this method is generally only used when the treatment site is on the high seas far from the coast. The best way to restrain oil spill pollution is to control the occurrence of oil spill accidents, which is much better than dealing with the foreseeable and unpredictable consequences caused by oil spill. However, oil spills always happen. In order to protect the ecological environment, we adopt various physical and chemical methods to deal with oil spill pollution, and the coastal ecological environment is the main goal of oil spill pollution control. Expansion: pollution caused by petroleum and its refined products (gasoline, kerosene, diesel oil, etc.). ) enter the marine environment in the process of mining, refining, storage, transportation and use. This is a serious worldwide marine pollution at present. Its prevention and control must rely on global cooperation to achieve more effectively. Oily wastewater from refineries is injected into the sea through rivers or directly; Oil spills, discharges and accidents of oil tankers make oil products directly enter the sea; Oil spill and blowout during the exploitation of submarine oil fields make oil enter the marine water body; Low molecular weight petroleum hydrocarbons in the atmosphere settle into seawater; Local natural oil leakage on the seabed. After oil enters the ocean, a series of complex changes will occur, including diffusion, evaporation, dissolution, emulsification, photochemical oxidation, microbial oxidation, sedimentation, asphalt ball formation, and transfer along the food chain. Changes after entering the sea Oil has undergone a series of complex changes after entering the sea, including diffusion, evaporation, dissolution, emulsification, photochemical oxidation, microbial oxidation, sedimentation, formation of asphalt balls, and transfer along the food chain. Although these processes are different in time and space, they are mostly interactive. Under the action of gravity, inertia force, friction force and surface tension, the oil diffused into the sea first expands rapidly into a thin film on the ocean surface, and then is divided into blocks or ribbon-shaped oil films with different sizes under the action of wind waves and currents, and drifts and diffuses with the wind. Diffusion is the main process to eliminate oil pollution in local sea areas. Wind is the most important factor affecting the oil spill drift on the sea surface, and the oil spill drift speed is about 3% of the wind speed. The oil slick found along the coast of Shandong Peninsula in China is more in the north bank of the peninsula in winter and more in the south bank of the peninsula in spring, which is also mainly caused by the influence of wind. Non-hydrocarbon components such as nitrogen, sulfur and oxygen in petroleum are surfactants, which can promote the diffusion of petroleum. During the diffusion and drift of evaporated oil, light components escape into the atmosphere through evaporation, and the rate varies with molecular weight, boiling point, oil film surface area, thickness and sea conditions. Most hydrocarbons containing less than two carbon atoms will evaporate and escape within a few hours after entering the ocean. Hydrocarbons containing 2 to 20 carbon atoms need several weeks to evaporate, while hydrocarbons containing more than 20 carbon atoms are not easy to evaporate. Evaporation is an important factor in the natural disappearance of marine oil pollution. Through evaporation, about 1/4 ~ 1/3 of the oil is discharged into the sea. The oil film oxidized on the sea surface undergoes autoxidation and photochemical oxidation under the catalysis of light and trace elements. Oxidation is the main way of petrochemical degradation, and its rate depends on the chemical characteristics of petroleum hydrocarbons. Within a few days after oil enters the sea, the processes of diffusion, evaporation and oxidation play an important role in the disappearance of oil in water, and the diffusion rate is higher than the natural decomposition rate. Dissolved low molecular hydrocarbons and some polar compounds can also be dissolved in seawater. The solubility of n-alkanes in water is inversely proportional to their molecular weight, and the solubility of aromatic hydrocarbons is greater than that of alkanes. Although both dissolution and evaporation are low molecular hydrocarbons effects, they have different effects on water environment. Petroleum hydrocarbons are soluble in seawater and easily absorbed by marine organisms, causing harmful effects. After emulsified oil enters the sea, it is easy to emulsify because of the agitation of water flow, vortex, tide and wind and waves. There are two forms of emulsification: water-in-oil emulsification and oil-in-water emulsification. The former is relatively stable, often gathering into blocks or spheres that look like ice cream and floating on the water for a long time. The latter is unstable and easy to disappear. If dispersant is used after oil spill, it will help to form oil-in-water emulsification, accelerate the removal of oil pollution on the sea surface and accelerate the absorption of oil pollution by organisms. After evaporation and dissolution, the oil deposited on the sea surface forms dense dispersed ions, which are polymerized into asphalt blocks or adsorbed on other particles, and finally settle on the seabed or float on the beach. Under the action of ocean currents and waves, oil or oil oxidation products that have sunk to the seabed can float to the sea surface again, causing secondary pollution. Marine biodegradation and absorption of petroleum hydrocarbons. Microorganisms play an important role in degrading petroleum hydrocarbons. Hydrocarbon oxidizing bacteria are widely distributed in seawater and submarine mud (see microbial degradation of petroleum hydrocarbons). Marine animals and plants can also degrade some petroleum hydrocarbons. Phytoplankton and sedentary algae can directly absorb or adsorb petroleum hydrocarbons dissolved in seawater. Marine animals will eat oil-adsorbed particles, and oil dissolved in water can enter the body through the digestive tract or gills. Because petroleum hydrocarbons are fat soluble, the content of petroleum hydrocarbons in marine organisms generally increases with the increase of fat content. In clean seawater, the oil accumulated in marine animals can be discharged relatively quickly. So far, there is no evidence that petroleum hydrocarbons can spread along the food chain. The speed and influence range of oil disappearing from the sea after it is discharged into the sea vary greatly due to the place where it enters the sea, the quantity and characteristics of oil, the methods of oil recovery and elimination, and the factors of marine environment. For example, a higher water temperature is beneficial to the disappearance of oil. Experiments show that it takes about one and a half months for oil to disappear from water at 0℃. When the water temperature rises to 20℃, it is 20 days; But at 25 ~ 30℃, it will drop to painting day. It is difficult to eliminate the oil that seeps into the sediment, and it takes several months to several years.