Introduction of Marine Aquaculture Cage Cleaning Technology

　　1. Current status of aquaculture cage culture

　　Cage aquaculture industry has experienced more than 30 years of development, from small-scale traditional aquaculture cages near the shore to the current intensive and large-scale deep-sea anti-wind and wave cages, and has developed through unremitting efforts of governments at all levels and scientific and technical workers It has become an emerging industry of aquaculture with a considerable scale in the coastal provinces.

　　As a large number of mariculture cages in China are concentrated in the harbor and near the shore, their water exchange is poor, and algae and microorganisms are seriously attached. It is poisonous and has many gaps. It can effectively protect the attached organisms, and its surface area is large relative to the volume ratio. During the breeding and feeding process, undigested fish, sea cucumbers, abalones, shellfish, etc. The accumulation of nutrients in the cage will also accelerate the growth of polluting organisms. The presence of fish excrement and residual bait provides sufficient nutrients for algae, bacteria, and microorganisms, and will also accelerate the growth of algae attached to the netting of cage. Due to the rapid growth of a large number of filamentous algae and other attachments, the net gear soaked in the water for a long time will soon block the mesh, resulting in a decrease in the water filtration performance of net cage, and a decrease in the dissolved oxygen in the water body in the net cage. The fluctuation is large, and the growth of cultured organisms in the cage is poor due to lack of oxygen or lack of plankton in the port, which affects the normal growth rate, feed efficiency, survival rate and unit yield of cultured organisms, especially with the cage culture. Aquatic products (such as sea cucumbers, abalones, steamed buns, eels, giant flounder, etc.) more serious.

　　In addition, aggravation of net clothing attachments in the net cage will also increase the overall weight of net cage, increase the resistance of net cage, and seriously affect the safety and service life of net cage. Therefore, biological pollution is a serious problem in marine aquaculture net cages. It is also a key problem that sea cage culture enterprises and individuals urgently need to solve.

　　2. The way of cleaning first is to expose to the sun or replace the net cage, which will cost a lot and cause great damage to the net cage.

　　2.1. There are two methods of manual cleaning: one is vibration cleaning. If suspended organic matter grows on the mesh of the cage, it can be cleaned in water. The operator will row the boat to one side of the cage and lift For netting, rub and shake by hand, or use a hard brush to scrub, or use a longer bamboo strip to whip. This kind of operation has a large workload and requires meticulous work to prevent bamboo strips and brushes from damaging the net clothing. It is suitable for small-scale farming by self-employed individuals; In the box, the nets are taken out of the water and transported to the shore to be piled up. After the attached algae rot, they are spread out and dried in the sun. They are cleaned on the shore by whipping and rolling, and then reassembled after checking that the net cage is intact. Compared with the previous one, the cleaning is thorough, but it is relatively more labor-intensive and destructive to the netting.

　　2.2. The mechanical cleaning method first requires the use of an engineering ship, which is equipped with a crane for lifting net cage. The ship is also equipped with a high-pressure cleaner, spray gun, rubber hose, etc., and the engineering ship is driven to the vicinity of net cage. Lift one side of net cage out of water with a crane, wash the dirt on the net cage with a high-pressure water gun, then change to the other side, and use the same method for cleaning. This method cleans more cleanly and reduces labor intensity, but this method is difficult to remove the animals attached to net clothes, and it is difficult to move the whole set of equipment, so it is not suitable for large-scale intensive breeding areas

　　2.3 Drug cleaning method of traditional drug cleaning method is to splash a certain concentration of copper nitrate on the net to kill the attached filamentous algae, but this method requires extremely high concentration when applying the drug, and their effect is not obvious when concentration is small. When the concentration is high, it will cause damage to aquatic products cultured in the cage. At present, there are also netting water-based anti-pollution coatings in the market. Its function is to prevent the climbing of aquatic organisms. This coating can prevent several types of aquatic organisms from climbing to a certain extent, but it cannot prevent all organisms from climbing 100%. There are many In addition, the action time of this kind of coating is limited, which greatly increases the cost of aquaculture.

　　3. Modern cavitation jet net cage cleaning equipment urgently needs to be used and popularized

　　Cavitation jet underwater cleaning technology, Cavitation refers to the formation of cavitation bubbles (that is, gas nuclei, the radius of which is generally below 20m) due to the evaporation of liquid due to the local low pressure of liquid flow system (lower than the saturated vapor pressure of the liquid at the corresponding temperature). Explosive growth, when the cavitation bubble stains are destroyed, it will cause a powerful micro-jet impact, resulting in a very short-lived high-pressure pulse, and the tiny space around the bubble will form a local hot spot, resulting in extreme high temperature and high pressure, accompanied by complex physical reactions, chemical reactions, Mechanical, electrochemical and thermal effects. According to calculations, when free cavitation bubble collapses, flow velocity of micro-jet near the wall can reach 70 to 180m/s, and the impact force generated on the surface of object is as high as 140 to 1Mpa, and the diameter of micro-jet is about 2 to 3m. The number of jet impacts is about 100 to 1000 times/(s cm2) Cavitation bubble bursting process

　　The cavitation jet cleaning technology is a new type of underwater facility cleaning technology formed by introducing cavitation into water jet cleaning technology, that is, artificially generating high-density cavitation bubbles in water jet beam, and using a large number of cavitation bubbles in the object The strong micro-jet impact force generated by the collapse of local micro-regions on surface can achieve the purpose of cleaning hard dirt and attached marine organisms. There is a cavitation jet underwater net cage cleaning equipment produced by SINPO., which is a single-disc rotary type. The machine mainly includes a high-pressure plunger pump driven by a diesel engine, a high-pressure connecting hose and a rotatable cleaning tray.

　　When cleaning net cages, high-pressure cleaning machine driven by diesel engine is placed on the boat, and water pump supplies water for it. The water inlet of high-pressure plunger pump is connected to the gasoline water pump with a quick joint, and water outlet of high-pressure plunger pump is connected to a high-pressure hose. Cleaning personnel hold the joystick connected to cleaning plate and stand on the edge of cage to perform cleaning work. When high-pressure water jet generated by high-pressure plunger pump passes through cavitation cleaning plate, high-density cavitation jet bubbles are generated. The reaction force generated in it pushes the cleaning disc to rotate, thereby generating a cavitation water jet circle to wash away the attached organisms on the cage. The length of joystick is adjustable, and maximum length is 1.5 meters, which fully meets the depth requirements of cage. The cavitation jet cleaning plate is made of stainless steel 316L, and special ceramic bearings are used inside, with high corrosion resistance, light weight and good structural strength. The rated working pressure of cleaning machine is 14MPa. The cleaning method of cleaning plate is simple. Its cleaning head is close to net and rotates and sprays. The cleanliness of cleaned area can be restored to more than 90%. Therefore, labor intensity is low and cleaning rate is high. Large-area net cage cleaning will not affect farmed aquatic products and will not cause environmental pollution.