Application of ozone in aquaculture water treatment
With the rapid development of the aquaculture industry, various advanced water treatment technologies have been widely used, such as sand filtration, microbial purification, ultraviolet sterilization, and foam separation. However, with the popularization and application of industrialized closed recirculating aquaculture equipment in actual production, the production conditions of high density and small water bodies have stricter requirements on water quality. Therefore, the application of high-efficiency and fast ozone technology for water quality treatment has emerged as the times require.
1. Characteristics of ozone
Ozone, also known as active oxygen, is an isomer of oxygen, easily soluble in water, and immediately undergoes a reduction reaction in water to produce intermediate substances, monoatomic oxygen and hydroxyl (OH), which have strong oxidizing ability, and hydroxyl is also a strong oxidant. , catalyst, therefore, ozone has a strong disinfection effect, and can decompose organic compounds that are difficult to destroy by general oxidants. The mechanism of disinfection by monoatomic oxygen and hydroxyl groups is: (1) Ozone can decompose the cell wall of bacteria, diffuse into human cells, oxidize Destroy the enzymes in the cells to kill the bacteria; (2) Ozone can react with the lipids of the bacterial cell wall, enter the bacterial body, act on lipoproteins and lipopolysaccharides, change the permeability of cells, and cause cell lysis. The ability of ozone to sterilize and decompose organic and inorganic substances in water is hundreds of times higher than that of commonly used chlorine. And because ozone is unstable, it is easy to generate oxygen and water after the reaction, so that it will not cause secondary pollution.
2. The basis that ozone can purify water quality
Due to the strong oxidizing properties of ozone, it has a good killing effect on various microorganisms in water. Wu Xuezhou et al. used ozone in a sterile hood (0.7m) and found that the killing rate of Escherichia coli was 97.5% and 100% when ozone was used for 20min and 30min; the killing rate of Staphylococcus aureus was 937% and 100%. %; the killing rate of Pseudomonas aeruginosa was 84.6% and 89.8%. Herbokd et al. reported that when ozone gas was passed into flowing water at 20 °C, when the ozone concentration in the water reached 0.43 mg/L, the large intestine could be destroyed. Bacillus 100% kill Zhai Falin et al reported that at 34℃±1℃, ozone with a concentration of 5.50mg/m can kill all the spores of Bacillus subtilis black var. The 1.5mg/L ozone solution can kill 100% of the fungi such as Aspergillus niger and yeast in the test in just 1 min. In addition, ozone also has a good killing effect on protozoa and their eggs.
3. Characteristics of ozone purification of water quality
- Due to the strong oxidizing properties of ozone, nitrite, hydrogen sulfide, ammonia cyanide, etc., which are more harmful to fish in freshwater or seawater for aquaculture, can be oxidized to non-toxic NO, SO, N, and other organic compounds. At the same time, inorganic substances can also be degraded to form non-toxic substances, thereby reducing biological oxygen consumption (BOD) and chemical oxygen consumption (COD) in water.
- The strong oxidizing property of ozone can quickly kill algae and other protozoa and plants. According to reports by Sun Xiaohong and others, after taking the red tide seawater for 30min ozone treatment, the red tide seawater was completely oxidized to become colorless and transparent, and noctilucents in the water were All were killed and shattered.
- Ozone can quickly and effectively kill the pathogenic bacteria in water that endanger the biological health of buffalo Kofich et al. The results show that 1rng/kg ozone can inactivate 90% of the cysts for 5 minutes. The same concentration of CIO, after the action of 1h, CI, and chlorine nitrogen can achieve the same effect only after the concentration is 80mg/kg and the effect is 90min.
- Since ozone is easily decomposed into 0 in water, it can not only play the role of sterilization and disinfection, but also oxygenate the water body, until it kills two birds with one stone.
- In the process of purifying water quality, ozone will not change the original composition of water. It can maintain the minerals in the water that are beneficial to aquatic animals
- While purifying the water source through ozone, it can also reduce the number of bacteria in the animal intestine that live on the host’s nutrition. Reduce the nutrient consumption of young bacteria, and enhance the activity of amylase secreted by beneficial bacteria, improve the utilization of food nutrients by animals, and promote the healthy growth of animals
- Ozone purifies water quality through oxidative flocculation without producing secondary pollutants. The oxides produced during the disinfection process are non-toxic, odorless and biodegradable substances.
4. Factors that affect the effect of ozone
- The concentration of ozone is within the allowable concentration. Generally, the higher the concentration of ozone, the faster the speed of killing bacteria, etc., the better the effect, but care should be taken not to make it excessive
- The ozone concentration of the same water temperature, at different water temperatures, the amount of dissolved in water is different. The lower the water temperature, the higher the solubility in water. For example, when it is 30, the solubility is 22%, and when it is 10, it is 54%. 0cc is 69%
- Inorganic ions in water When there are many inorganic ions in water, it will accelerate the decomposition of ozone, thereby reducing the concentration of ozone and hindering the efficiency of sterilization.
- Turbidity in water It is reported that when the turbidity of water is below 5mg/L, it has little effect on the sterilization effect of ozone, but when the turbidity is above 5mg/L, it has an impact. Because a large part of ozone is used for the oxidative decomposition of organic and inorganic substances at this time
5. Toxic and side effects of residual ozone in water to aquatic organisms
Jiang Guoliang et al. (2001) showed in the acute toxicity test of ozone on flounder and shrimp that when the residual ozone concentration was 0.2-0.4 mg/LH~ after 12h, the survival of flounder was 65%; at 24h, it was 47%; At 48h, it was 23%; when the concentration increased to 0.5-0.8ml/L, no one survived at any time, Reid. B (1994) study shows that the ozone concentration of 1-5mg/1 is the lethal concentration of shrimp. The Hubbs study found that the toxic reaction of fish when the residual ozone concentration is high, mainly abnormal movement and respiration, followed by loss of balance, and the fish sometimes swims and sometimes rests. Therefore, although ozone can significantly purify water quality and increase the output of fish and shrimp, its toxic effects on aquatic organisms such as fish and shrimp cannot be ignored. Use small doses (usually 0.05 ~ 0.3mg/L) and short time (0.3 ~ 2min) contact. To sum up, due to the advantages of ozone itself, such as wide sterilization spectrum. The effect is fast and thorough, and there is no secondary pollution. It can purify water quality by decomposing inorganic and organic matter, etc., and can increase dissolved oxygen. Therefore, ozone is an ideal sterilizer and disinfectant, which can be widely used in the treatment of aquaculture and domestic water quality. Ozone can significantly improve water quality. When used in a recirculating aquaculture system, it can save a lot of water and reduce the heat energy consumed for temperature control. Therefore, in the long run, the application of ozone for water quality treatment can be regarded as an economical and effective water treatment method.
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