Oxygenation technology for land-based industrialized recirculating aquaculture

Maintaining an appropriate level of dissolved oxygen is crucial for the healthy growth of fish in a factory farming system. Generally speaking, in order to ensure the normal growth of fish, the dissolved oxygen in water should reach at least 60% of the saturation solubility, which means that each liter of water contains at least 5 milligrams of dissolved oxygen. When the concentration of dissolved oxygen is below 2 milligrams per liter, the nitrifying bacteria that treat water will not be able to effectively nitrify ammonia nitrogen, thereby affecting water quality and the living environment of fish.

The consumption of dissolved oxygen in industrialized aquaculture systems mainly comes from the metabolic activities of fish, the decomposition of metabolic products, and the treatment of ammonia nitrogen by microorganisms. The dissolved oxygen required by the system will also vary depending on the type of fish being farmed. At the same time, with the increase of breeding density and the addition of bait, the demand for dissolved oxygen will also correspondingly increase. Therefore, in the process design of industrialized aquaculture, it is necessary to comprehensively consider multiple factors such as the breeding object, breeding density, and water circulation to develop a reasonable oxygenation plan.

1. Air oxygenation

In factory aquaculture ponds, the use of large oxygenation machinery is often limited due to space and environmental conditions. Therefore, air oxygenation usually uses a fan combined with an aerator to increase the dissolved oxygen content of the water by generating small bubbles. This method is easy to operate and requires less investment, but the oxygenation efficiency is relatively low. For example, at 20 ℃, its oxygenation efficiency is about 1.3 kilograms of oxygen per kilowatt hour, while at 28 ℃ it drops to 0.455 kilograms of oxygen per kilowatt hour. Therefore, the breeding density of this method can usually only reach 30-40 kg/cubic meter. In order to improve the efficiency of oxygenation and reduce costs, it is particularly important to research and develop specialized oxygenation equipment suitable for factory farming.

2. Pure oxygen oxygenation

Pure oxygen oxygenation is an efficient method of oxygenation, which mainly comes from three sources: oxygen cylinders, liquid oxygen tanks, and pure oxygen generators. However, simply injecting pure oxygen into water through an aerator can result in a significant amount of oxygen waste. In fact, only about 40% of pure oxygen can be effectively utilized in this way, while the remaining oxygen will escape from the water surface and be wasted. Therefore, in order to fully utilize pure oxygen and improve oxygenation efficiency, specialized equipment and technical means must be used.

3. Microbubble oxygenation

In order to improve the efficiency and utilization of oxygen, researchers have turned their attention to microbubble oxygenation technology, which mainly focuses on how to generate small bubbles to increase the gas-liquid contact area and promote the dissolution and absorption of oxygen. Some scholars have studied the formation and dissolution process of oxygen bubbles in water to determine the optimal bubble size. For example, a research team from the University of Tokyo in Japan successfully generated microbubbles with an average diameter less than 20 microns using ultrasonic technology, significantly improving the efficiency and quality of oxygenation treatment.

Dissolved oxygen, as a key factor for the survival of aquatic organisms, is of great importance. With the continuous development of aquaculture and the popularization of factory farming models, research and innovation in oxygenation technology have become particularly important. The application of advanced technologies such as air oxygenation, pure oxygen oxygenation, and microbubble oxygenation has seen a revolutionary change brought by technology to the aquaculture industry. In the future, with the emergence and application of more new technologies, we are expected to achieve more efficient and environmentally friendly aquaculture models and contribute to the sustainable development of humanity.