An aeration machine is a mechanical device that increases the dissolved oxygen in water bodies. It keeps the aquaculture water bodies with sufficient dissolved oxygen, promotes the proliferation of aerobic microorganisms, reduces ammonia nitrogen and other organic substances, improves water quality, and is conducive to intensive and high-yield aquaculture.
The aeration principle is that during the transfer of gas into liquid, molecular diffusion occurs in the gas-liquid double membrane, and convective diffusion occurs outside the membrane. The aeration machine achieves the purpose of increasing the dissolved oxygen in the aquaculture water body by stirring the interface between gas and liquid, increasing the speed of relative motion between the gas and liquid phases, and accelerating the diffusion and transfer of oxygen.
The main types include impeller type, water wheel type, water spray type, jet type, propeller type and air injection type. In addition, there are also pipe type, suction type and gravity type, etc. The selection depends on the aquaculture objects and water body conditions.
Impeller type
The impeller and reducer are the key components of the impeller aeration machine. The types of impeller include inverted umbrella type, pump type and flat plate type. Among them, the inverted umbrella type has a simpler structure, stronger water lifting capacity, better aeration effect, and a power efficiency of 1.4 to 2 kilograms of oxygen per kilowatt-hour. The pump type has a strong water lifting capacity and good aeration effect, but the structure is more complex and it will cause pits on the muddy bottom of the pond, so it is less used. The flat plate type has a simpler structure, but the water lifting capacity is weak and the aeration effect is poor. The material of the impeller includes steel, fiberglass, engineering plastics, etc. The impeller plays the role of lifting water and transporting water. When the impeller rotates, the diffused water flow formed around it comes into contact with the air, and the negative pressure at the rear side of the impeller causes air to be sucked in and continuously updated to increase dissolved oxygen.
Principle: The impeller sucks up the oxygen-poor water at the bottom and pushes it out to the surrounding areas, turning stagnant water into flowing water. The water under the impeller is strongly stirred by the blades and pipes, and water splashes and waves are formed on the water surface, forming a water curtain that can carry in air. Due to the negative pressure formed at the rear of the impeller during rotation, air can be sucked into the water through the stirring pipe and immediately be broken into micro-bubbles and enter the pressure zone of the impeller, which is also conducive to increasing the dissolution speed of oxygen in the air and improving the aeration efficiency.
Advantages: 1. Water lifting and stirring. The impeller type aeration machine can lift the bottom water and make it alternate with the surface water, thus achieving the effect of oxygenation in the bottom water. Its aeration depth exceeds 2 meters; 2. The mechanical structure is relatively simple, and there are few mechanical failures during use, making maintenance convenient and reducing maintenance costs; 3. During use, it can form middle and upper layer water flow, making the dissolved oxygen in the middle and upper water bodies uniform, suitable for pond aquaculture and emergency equipment in ponds; 4. Remove harmful gases. The impeller type aeration machine has a strong aeration function, and harmful gases such as ammonia, hydrogen sulfide, methane, and carbon monoxide in the pond water can be effectively removed.
Disadvantages: 1. It can only be used when the power supply is smooth. In remote areas with insufficient electricity, laying wires is costly; 2. The aeration machine usually must be fixed at one point in the pond, changing positions is troublesome, and the aeration area is limited to a certain range, resulting in poor oxygenation effect for the bottom water in larger ponds; 3. The floating cylinder of the aeration machine is exposed to the air all year round, and it is prone to corrosion and damage due to sun exposure, requiring frequent replacement; 4. It is single-point aeration, and the mechanical operation noise is large, which may affect the growth of aquatic animals and cause injuries to aquatic animals; 5. The impeller aeration machine is prone to sucking up the bottom mud, and is not suitable for use in ponds with shallow water levels.
Water wheel type
The impeller is an assembly of the hub and blades, and the hub is mostly made of aluminum casting, or cast iron or injection molded parts. The blades are mostly made of aluminum casting or injection molded parts. The floating body is made of foam plastic, fiberglass or plastic pipe. The reducer box is driven by a two-stage cylindrical gear transmission. The water lifting effect of the water wheel type is weak, while the pushing water effect is strong, causing the water body to flow in a unidirectional manner and a large amount of water droplets are thrown into the air. The power efficiency is 1.2 to 1.75 kilograms of oxygen per kilowatt-hour, and it is mainly used in eel ponds, shrimp ponds, etc.
Principle: Two rectangular floating boxes are used as the buoyancy devices. The motor is installed on the floating box, driving the vertical impeller in the middle to generate water waves, thereby achieving the effect of oxygenation.
Advantages: 1. The overall weight is relatively light, the structure is relatively simple, the cost is low, and the oxygenation effect is good in shallow ponds; 2. It has strong mixing ability in the middle and upper layers and certain mixing ability, can obtain a better contact area between oxygen and water, and has high oxygenation efficiency; 3. When more than two water wheel-type oxygenators are arranged in the pond, a directional flow can be formed throughout the pond.
Disadvantages: 1. The upward force for the bottom is not strong enough, and the oxygenation effect in deep water areas is not ideal; 2. It is not suitable for emergency use when aquatic animals float to the surface.
Spray type
It consists of a submersible pump, spray head, and floating body support. The spray head is a reverse cone shape, usually a single spray head, but there are also double and triple spray heads. The floating body is circular and made of thin steel plate or foam plastic. When working, the water sprayed into the air comes into contact with the air, allowing oxygen to dissolve in the water. The power efficiency is generally 0.45 to 0.8 kilograms of oxygen per kilowatt-hour.
Principle: The lower part of the water in the pond is pumped up and sprayed out in a high-speed manner in all directions or forward.
Advantages: 1. It can extend and expand the time and area of air aeration and oxygenation; 2. It has a good oxygenation function, can rapidly increase the dissolved oxygen content in the surface water layer in a short time, and also has an artistic viewing effect, suitable for use in fish ponds for landscaping or tourism areas.
Disadvantages: Due to its small effective oxygenation area and poor energy conversion efficiency, it is currently only applied in parks, tourist fish ponds, and small ponds, being both beautiful and practical.
Jet type
It consists of a submersible pump, distributor, and jet device (including nozzle, suction pipe, mixing pipe, and diffusion pipe). The pressure water output by the pump is divided and enters the jet device through the distributor, and is ejected at high speed through the nozzle. In the surrounding area, a negative pressure is formed and air is sucked in through the suction pipe. The air and water in the mixing pipe and diffusion pipe are compressed, mixed vigorously, and compressed into tiny bubbles, increasing the contact surface between the bubbles and water, accelerating the dissolution of oxygen. The power efficiency is generally 0.5 to 0.8 kilograms of oxygen per (kW·h). It can be used in live fish transportation boxes or jet oxygenation boats.
Principle: The centrifugal pump rotates to suck the oxygen-deficient water at the bottom of the pond and pressurize it, accelerating the input into the jet device. When the water is ejected from the nozzle, it forms a high-speed water column jet, which is injected into the pond water and generates convection with the water body, achieving the effect of oxygenation for the pond.
Advantages: 1. The structure is simple, and it can form water flow and stir the water body; 2. The jet-type oxygenator can evenly oxygenate the water body smoothly, without damaging the fish, and is suitable for oxygenation in fish seedling ponds.
Disadvantages: The oxygenation effect is not ideal. In actual production, it is often made into a jet oxygenation feeding boat to achieve the dual effect of feeding and oxygenation. The oxygenation area is small, and it is prone to pushing the bottom up.
Propeller type
The shape of the propeller is similar to a propeller or axial flow pump impeller. The motor is directly driven by the propeller, and the structure is simple. When rotating, the propeller generates vortices and pushes out a large amount of water, forming a thick water film covering the air and creating waves on the water surface. The power efficiency is 0.8 to 1.2 kilograms of oxygen per (kW·h). The most common one is the surging machine.
Principle: The surging machine is a new type of pond aquaculture oxygenation machinery developed and promoted in recent years. Its working principle is to use the floating body impeller to lift water in the center and resonate to create waves in all directions.
Advantages: 1. Simple design, lightweight, and energy-saving; 2. It can increase the light intensity of sunlight on the water body and the contact area between gas and liquid, promoting the growth of algae, and fully and effectively utilizing the ecological oxygenation capacity of the pond; 3. The oxygenation capacity is strong in good weather conditions.
Disadvantages: 1. If the pond is too shallow, the surging waves may be too large and muddy the water; 2. The oxygenation capacity is generally poor in rainy days. There are many types of air diffusers, which are laid on the bottom of the pool. They are evenly distributed with small holes, micropores or variable holes. The air from the compressor passes through the air pipe and is dispersed from the small holes of the air diffuser. The air dissolves in the water. The most common type is the Roots blower.
Principle: The Roots blower is used to send air into the air pipe, which then sends the air into the micropore pipe. The micropore pipe disperses the air in the form of micro-bubbles into the water. The micro-bubbles rise from the bottom of the pool and are affected by the high oxygen pressure of the gas, allowing oxygen to be fully dissolved in the water. It can also cause the water flow to rotate and move up and down. The up and down movement of the water flow brings the oxygen-rich water from the upper layer to the lower layer, while the rotational movement of the water flow spreads the oxygen-rich water around the micropore pipe outward, achieving uniform oxygenation of the pool water.
Advantages: 1. Energy saving. The pressure of the bottom micropore aeration machine is wide, the structure is simple, maintenance is convenient, the service life is long, and the vibration of the whole machine is small. Practice has proved that the underwater aeration and oxygenation effect is good. Compared with traditional oxygenation methods, achieving the same effect can save 60-80% of electricity. A high-performance oxygenation equipment with a power of 2.2 kilowatts can effectively oxygenate 30-40 acres of water surface; 2. Improving the ecological environment of the aquaculture water body. The air bubbles generated at the bottom of the water body by aeration and oxygenation have a wide range of flow, and sufficient air flow contacts the large area of the water surface, ensuring that the dissolved oxygen in the bottom of the water body reaches 6.5 milligrams per liter, accelerating the oxidation and decomposition of harmful substances such as organic matter and nitrite in the bottom of the water body, and carrying out harmful and toxic gases out of the water surface, thereby improving and stabilizing the water quality, creating a suitable growth environment for fish, shrimp, and crabs, and reducing the occurrence of diseases; 3. Beneficial for high-density aquaculture. Aeration and oxygenation by aeration and oxygenation is static aeration at the bottom of the water body, providing sufficient dissolved oxygen in all layers of the water body, improving the activity ability of breeding objects in all layers of the water body, increasing appetite, shortening the breeding cycle, and creating conditions for increasing the biological load of the water body; 4. Easy to use. Different water surface areas can be equipped with different power blowers. One blower can be used for double-basin aeration or multi-basin aeration. The main pipe and branch pipes can be connected and replaced easily; 5. No electricity leakage in the water. Compared with traditional oxygenation machines, the bottom micropore aeration is laid in the water, the motor is on the shore, and there is no possibility of electricity leakage in the water.
Disadvantages: 1. The initial investment cost is higher compared to impeller-type and other aeration machines; 2. The current micropore technology level is limited, and the produced aeration pipes are prone to clogging; 3. It is not suitable for deep water ponds. Generally, for ponds with a water depth of more than 1.5 meters – 2.0 meters, the water pressure is too high to achieve good oxygenation effect.
Scientific use of aeration machines
Firstly, the scientificity and principles of using aeration machines should be clear. The commonly mentioned “three on” and “two not opening” are the principles. Acting according to the principles is scientific and can avoid.
Three on：
1. Start the aeration machine in the afternoon after a sunny day. The oxygen source in the pond mainly comes from the photosynthesis of phytoplankton. After noon， the oxygen content in the water reaches saturation. Turn on the aeration machine for about 1 hour from 12：00 to 14：00， which can bring the oxygen-deficient water layer at the bottom and potential “flooding factors” – organic substances deposited at the bottom to the upper layer and merge with the oxygen-rich surface water， breaking the thermal layer and eliminating the risk of flooding， even in the event of a change from south wind to north wind or thunderstorm weather at night， the loss can be minimized. The shutdown time should not be too late. After shutting down， if the organic matter in the upper layer is still difficult to be completely decomposed， the dissolved oxygen produced by photosynthesis in the afternoon can be further decomposed to maintain the high dissolved oxygen state of the entire pond water.
- Start the aeration machine before dawn the next day on cloudy days. On cloudy days， due to weak photosynthesis， the aeration machine has no oxygenation effect during the day. After the night’s consumption， generally， ponds with a high fertilizer level or a high stocking density of breeding animals may be oxygen-deficient before dawn. At this time， starting the aeration machine can directly bring the oxygen in the air into the water to solve the oxygen deficiency problem.
The third situation is to start the machine when there is continuous rainy weather or when there is a serious risk of oxygen deficiency due to algal blooms, etc. The machine must be started before the oxygen deficiency occurs and also at night around 9:00 PM. Moreover, for ponds with aquatic plants (such as crab ponds), if the number of aquatic plants is excessive and there is a large amount of bubble rise in the afternoon, it is advisable to start the aeration machine around 9:00 PM at the latest. Once the machine is started, it must not be stopped halfway and should continue until after sunrise.
Two Do Not:
1. Do not start the machine in the evening. If it is not the third situation, the evening is generally not a period of oxygen deficiency. If the machine is started at this time, it may have the opposite effect because photosynthesis stops at night, and the dissolved oxygen in the water will show a process from high to low throughout the night. Maybe there will be no oxygen deficiency throughout the night, or it may start to become oxygen-deficient in the early morning. At that time, it is only necessary to start the aeration machine for a short period to solve the problem. If the pond has oxygen deficiency only in the early morning and starts the aeration machine in the evening, it will stir up the bottom layer of anaerobic water and organic substances to the surface, accelerating the consumption of limited dissolved oxygen. If it does not stop the machine until after sunrise the next day, it will cause the pond to become oxygen-deficient due to lack of oxygen, not only wasting manpower and electricity, but also causing greater economic losses.
2. Do not start the machine during the day on rainy days. Because there is insufficient light and weak photosynthesis on rainy days, the dissolved oxygen in the water surface layer is difficult to reach saturation. Starting the aeration machine will not only stir up the bottom sediment and increase oxygen consumption, but also disrupt the photosynthesis process of phytoplankton, causing the pond water to enter the oxygen-deficient period earlier at night.
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