Nitrogen cycle in recirculating aquaculture system

Nitrogen is a very important element in living organisms. It is one of the main components of protein. All living organisms contain protein. Proteins are composed of different numbers of peptide chains. Each peptide chain is composed of multiple amino acid molecules. Therefore, amino acids are the basic unit of protein. Amino acids all contain three elements: carbon, hydrogen and oxygen. Some contain sulfur, phosphorus and other elements. In this section, we will mainly talk about the cycle process of nitrogen in the recirculating aquaculture system.
First of all, in a relatively fixed-density aquaculture water body, except for the necessary evaporated water, other substances will not disappear or be produced. The variables mainly come from the fish food put into the water and various wastes discharged from the sewage. Of course, the amount of fish input will be greater than the amount of waste discharged from the entire site. Part of this difference is the consumption of the organism itself, and part of it becomes the organism's body-they will change from small fish to big fish. This is the meaning of recirculating aquaculture. We not only pursue the total amount of fish produced, but also pay attention to the speed of their production. Among the customers of Lanling Aquarium, some recycled aquaculture farms of Penaeus vannamei can produce shrimps in three seasons or even four seasons a year. The economic benefits are considerable.
When nitrogen is present in fish feed, it generally exists in the form of protein. After being fed, most of them will be eaten by fish, and a small part of uneaten feed will be scattered in the aquaculture water. Under the action of decomposing bacteria, they are gradually converted into amino acids, and then further converted into ammonia. The part eaten by the fish is digested by the fish and converted into ammonia. Ammonia, which has the same goal in different ways, is a substance that is easily soluble in water. It will produce ammonia ion and hydroxide ion after hydrolysis. But this chemical reaction is a reversible reaction. When the concentration of hydroxide ions in the water is high, the reaction proceeds to the left, and the concentration of ammonia molecules will increase. The opposite is the same. Under the action of nitrifying bacteria, ammonia is converted into nitrite. Nitrite is a less stable substance. In the case of high redox potential, it will be oxidized to nitrate. At this time, if there are denitrifying bacteria, nitrate will be denitrified into nitrogen. In this way, the nitrogen added in the water body completes a complete conversion process.

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