Marine fouling organisms, also known as marine attached organisms, are animals, plants, and microorganisms that grow on the bottom of ships and on the surfaces of all facilities in the sea. These organisms are generally harmful. The organisms on the bottom of the ship are called biofouling, and preventing biofouling is called anti fouling. Biological fouling is a biological hazard that humans have encountered since the beginning of contact with the ocean. The harm of fouling organisms to ships and pipelines has long attracted great attention. In recent years, with the development of the marine industry and shipbuilding industry, the attachment and fouling of marine organisms have attracted great attention. During the season of vigorous growth and reproduction of marine organisms, it may take only 1-2 months for marine organisms to grow on the surface of ship hulls, seawater cooling systems, and other buildings. Research has shown that marine organisms have a significant impact on the corrosion rate of carbon steel and low-alloy steel. The attachment of organisms makes it difficult for valves to function properly, resulting in a decrease in the flow rate of cooling water through seawater pipelines and coolers, a decrease in the heat exchange efficiency of coolers, and an increase in fuel consumption. Sometimes ships have to stop for cleaning work, and sometimes equipment and instruments are damaged, rotating parts fail, causing serious accidents and huge economic losses to people.
2, Anti pollution treatment technology
After scientific research, more than ten methods have been summarized to prevent the attachment of marine organisms. Although they all have certain limitations, they are all effective and have varying degrees of value.
1. Apply anti fouling paint
Anti fouling paint is composed of toxic materials, pigments, paints, solvents, additives, etc. Toxic materials are the most important component. The commonly used toxic materials are toxic mercury compounds, while other commonly used toxic materials include DDT and various organotin compounds. Its function is to continuously seep out of the paint film with toxic materials, forming a toxic thin layer on the surface of the structure, repelling or killing the spores or larvae of marine organisms attempting to stay on the paint film. Copper ions, mercury ions, and other substances have the ability to coagulate proteins in organic matter, achieving the goal of anti fouling.
2. Add a large amount of toxins to seawater
The main toxic materials are liquid chlorine, bleach powder, etc. By utilizing the strong oxidizing properties of these substances, organic matter is oxidized, causing damage to marine organisms and leading to their death.
3. Electrolysis of seawater to generate hypochlorite
Seawater contains a large amount of chloride ions. By using special electrodes to apply direct current, seawater can be electrolyzed to produce sodium hypochlorite. Low concentrations of sodium hypochlorite in seawater can damage the cellular tissues of marine organisms, causing death or loss of attachment ability of larvae, larvae, spores, etc.
4. Electrolytic heavy metal method
Many heavy metals are toxic, and the most commonly used method for electrolyzing copper or alloys is to install copper anodes in seawater and electrolyze them into copper ions through direct current to dissolve them in seawater. Copper ions are toxic materials that can reduce the attachment of many animal and biological species, playing a role in anti fouling.
5. Manual or mechanical removal method
This is a measure taken for structures that have already attached organisms, usually using non work line manual or mechanical removal during normal shutdown periods, mainly targeting non spinal animals. The use of this method to solve fouling problems still accounts for a large proportion.
6. Filtering method
This method involves digging deep water wells at the seaside and utilizing the filtering effect of soil, gravel, and other materials to remove marine organisms such as eggs, spores, and larvae, thus avoiding their growth in the seawater transport system.
7. Heating method
It is to supply hot water (or hot alkaline water) into the seawater transportation system that has already attached marine organisms. When the temperature reaches 50'C and lasts for half an hour, the attachments can be killed. Then, a large amount of seawater is used to clean the pipeline and remove debris.
8. Closed method
Block both ends of the pipeline with attached organisms. Due to lack of oxygen and bait, the marine organisms will die on their own after a few days. Then flush the pipeline and remove the debris.
9. Utilize freshwater
Due to changes in the living environment, marine organisms die on their own. Some ships navigate back and forth between the ocean and rivers, causing marine or freshwater organisms to die. However, their debris accumulates in pipelines and must be cleaned up in a timely manner.
10. Using anti fouling lining to make structures
According to the performance requirements of the structure, suitable metals or alloys are selected to make the structure. The toxicity of the structure itself is utilized to hinder the attachment of fouling organisms. For example, the anti fouling copper alloy is used to make the interception grille of the water intake head. Toxic metals include silver, arsenic, copper, lead, tin, cadmium, nickel, zinc, mercury, drill, etc.
11. Increase the motion speed of submerged objects
Static submerged objects cause the most severe fouling. Experiments have shown that when the seawater flow rate on the surface of the structure reaches 2.9-8.5 nautical miles per hour, all animal fouling is affected to some extent. When the speed reaches 11 nautical miles per hour, the attachment of algae is affected.
12. Stinky ammonia method
In recent years, while chemical resistance treatment has been deeply developed, a new and innovative ozone based cooling water treatment technology is emerging abroad. People have found that adding ozone to cooling water can not only kill bacteria and viruses in the water, but also inhibit or eliminate scaling. Controlling equipment corrosion without the need for adding any chemicals, without adjusting pH value, without polluting the environment, and with low operating costs, is increasingly attracting people's attention.
Compared to chlorine, ozone not only has a stronger broad-spectrum biological effect, but also has a faster killing rate than chlorine. The research results show that the sterilization rate of ozone is 3125 times faster than that of chlorine gas, which means that if an appropriate concentration of ozone is selected, the killing rate of ozone is measured in seconds, while the killing rate of chlorine is measured in hours. Compared with chlorine, ozone not only has a stronger ability to oxidize and destroy biological enzymes, but also diffuses and penetrates the cell wall faster than chlorine. Therefore, it naturally has greater killing power than chlorine. Practice has proven that using ozone to treat wastewater does not require the use of non oxidizing biocides, thus avoiding concerns about environmental pollution.
It can be seen that the ozone method is not only technically feasible, but also very economical. However, it should be pointed out that the ozone treatment method is still in the development stage, and its mechanism of action is not very clear. The technology still needs further improvement, and it is difficult to predict whether it can replace chemical methods. However, as a unique cooling water treatment method, it still has vitality and should be developed and utilized according to the specific situation in China.