With the rapid development of aquaculture in China, various advanced water treatment technologies have been widely used, such as sand filtration, microbial purification, ultraviolet disinfection and foam separation. However, with the popularization and application of industrialized closed circulating water aquaculture equipment in actual production, the production conditions of high density and small water body have stricter requirements on water quality. Therefore, the technology of using ozone with high efficiency and rapidity to treat water quality came into being.
1 characteristics of ozone: ozone (O3), also known as active oxygen, is an isomorphism of oxygen, which is easily soluble in water, and immediately undergoes a reduction reaction in water, producing intermediate monoatomic oxygen and hydroxyl (H). The oxidation ability of monoatomic oxygen is very strong, and hydroxyl is also a strong oxidant and catalyst. Therefore, ozone has a strong disinfection effect and can decompose organic monoatomic oxygen and hydroxyl which are difficult to be destroyed by general oxidants. The mechanism of disinfection is as follows: (1) (2) Ozone can react with lipid bonds in bacterial cell walls, enter the interior of bacteria, act on fatty egg whites and lipopolysaccharides, and change the permeability of cells, thus leading to cell lysis. The ability of ozone to sterilize and decompose organic matter and inorganic matter in water is hundreds of times higher than that of commonly used chlorine. Moreover, due to the instability of ozone, oxygen and water are easily generated after the reaction, which will not cause secondary pollution.
2 ozone can purify water. Because of its strong oxidation, ozone has a good killing effect on various microorganisms in water. Wu Xuezhou et al. introduced ozone into the sterile cover (．7m), and found that the killing rates of Escherichia coli were 97.5% and 1% after 2min minutes and 3min minutes of ozone. The killing rates of Staphylococcus aureus were 93.7% and 1%. The killing rate of Pseudomonas aeruginosa was 84.6% and 89.8%. Herbokd et al. reported that when ozone gas was introduced into flowing water at 2℃, Escherichia coli could be 1% killed when the ozone concentration in water reached .43 mg/L. Zhai Falin et al. reported that at 34℃ 1℃, It is reported by Bai Xiyao and others that ozone with concentration of 5.5 mg/m can kill all spores of Bacillus subtilis var. Niger dripped in 1ml plastic bottles within 45 minutes, and the fungi such as Aspergillus Niger and yeast can be killed by 1.5 mg/L ozone solution in the experiment only in 45min. In addition, ozone also has a good killing effect on protozoa and their eggs.
3 characteristics of ozone in purifying water quality 3.1 Due to the strong oxidation of ozone, nitrite, hydrogen sulfide and cyanamide, which are harmful to fish in fresh water or seawater for aquaculture, can be oxidized into non-toxic NO, SO, N and other organic substances, and inorganic substances can also be degraded to produce non-toxic substances. So as to reduce the biological oxygen consumption (BOD) and chemical oxygen consumption (COD) in the water < P > 3.2 The strong oxidation of ozone can quickly kill the original vivid plants such as algae. According to Sun Xiaohong and other reports, after taking red tide seawater for 3 minutes of ozone treatment, the red red tide seawater is completely oxidized to be colorless and transparent, and all the noctilucent insects in the water are killed and crushed.
3.3 Ozone can quickly and effectively kill the pathogenic bacteria that are harmful to buffalo's biological health. Kofich and others compared the killing effects of ozone, CIO, CI, and chlorine nitrogen on Cryptosporidium smiling eggs. The results showed that 9% of the cysts could be killed by ozone with lrng/kg for 5 minutes, while CIO with the same concentration, lh, CI and chlorine nitrogen were all at 8mg/kg and acted for 9 5min. 3.4 Because ozone is easily decomposed into zero in water, it can not only play the role of sterilization and disinfection, but also make the water oxygenated until it can kill two birds with one stone. 3.5 In the process of purifying water quality, ozone will not change the original components in the water. It can keep the minerals beneficial to aquatic animals contained in the water. 3.6 While purifying the water source through ozone, it can also reduce the number of bacteria living on host nutrition in the intestinal tract of animals and reduce the nutritional consumption of young bacteria. Moreover, the activity of amylase secreted by beneficial bacteria is enhanced, the utilization effect of food nutrients by animals is improved, and the healthy growth of animals is promoted. 3.7 Ozone can purify the water quality through oxidation flocculation, and will not produce secondary pollutants. The oxides produced in the disinfection process are nontoxic, odorless and biodegradable.
4 factors affecting the ozone action effect 4.1 The concentration of ozone is within the allowable concentration. Generally, the higher the concentration of ozone, the faster the bacteria will be killed and the better the action effect will be. However, care should be taken not to make it exceed 4.2. The same ozone concentration at the temperature of water, and the amount dissolved in water is different at different water temperatures. The lower the water temperature, the higher the solubility in water, such as 3, the solubility is 22%, and the solubility is 54% at lO. CC is 69%. 4.3 Inorganic ions in water will accelerate the decomposition of ozone when there are more inorganic ions in water, thus reducing the concentration of ozone and hindering the efficiency of sterilization. 4.4 Turbidity in water is reported to have little effect on ozone sterilization when the turbidity of water is below 5mg/L, but when the turbidity is below 5 mg. At this time, a large part of ozone is used for the oxidative decomposition of organic and inorganic substances.
5 Toxic side effects of residual ozone in water on aquatic organisms. Jiang Guoliang et al. (21) showed in the acute toxicity test of ozone on PARALICHTHYS olivaceus and prawn that when the concentration of residual ozone is .2 ~ .4 mg/LH ~ after l2h, PARALICHTHYS olivaceus survives by 65%. 47% at 24h; 23% at 48h; When the concentration increased to .5 ~ .8 ml/L, no one survived at any time. Reid B (1994) showed that the ozone concentration of l-5mg/1 was the lethal concentration of shrimp. Hubbs research found that the toxic reaction of fish when the residual ozone concentration is high is mainly abnormal movement and breathing, and then it loses balance. The fish sometimes swims and sometimes stands still, and when it stands still, the side or belly of the fish faces up, which eventually leads to the death of the fish. Therefore, although ozone can significantly purify the water quality and increase the output of fish and shrimp, its toxic effect on aquatic organisms such as fish and shrimp can not be ignored, so it should be rinsed according to the actual situation in practical application. To use a small dose (generally .5 ~ .3 mg/L) and a short time (.3 ~ 2 min) for contact-To sum up, ozone is an ideal disinfectant because of its own advantages, such as wide bactericidal spectrum, rapid and thorough action effect, and no secondary pollution. Water quality can be purified by decomposing inorganic substances and organic substances, and dissolved oxygen can be increased. It can be widely used in the water quality treatment of aquaculture and domestic water, and ozone can obviously improve the water quality. When it is used in the circulating aquaculture system, it can save a lot of water and reduce the heat energy consumed for temperature control. Therefore, in the long run, it is an economical and effective water treatment method to apply ozone to water quality treatment.