| With the continuous development of China’s aquaculture industry,the industrialization and scale of aquaculture have been continuously improved,and the application of high-density aquaculture has become more and more extensive,which has created new challenges for aquaculture oxygenation.The conventional oxygenation method with air as the medium can no longer effectively solve the problem of water hypoxia in summer high temperature conditions,and new oxygenation methods need to be explored.In this paper,aiming at the pond captive mode,the gas-liquid mixing pump is used as the core device,and the pure oxygen is used as the medium to build the oxygenation system.The dissolved oxygen performance of the gas-liquid mixing pump is tested,and the oxygenation test is carried out in the captive barrel of the pond captive platform to verify the feasibility of the gas-liquid mixing pump combined with pure oxygen oxygenation.Phytoplankton in ponds have significant photosynthesis under high temperature and strong light in summer.Light is the main factor affecting the photosynthesis of aquatic plants in summer.Combined with the advantages of LED lights and successful application cases in plant factories,LED lights were used to explore the effect of light on the oxygenation of biological light in water in dark environment.The specific work contents and research results are as follows:（1）The dissolved oxygen performance test platform of gas-liquid mixed pump was built.The dissolved oxygen performance of gas-liquid mixed pump was tested under different water temperature,different water pressure and different gas-water ratio.The results of dissolved oxygen performance test show that the dissolved oxygen concentration in oxygen-enriched water produced by gas-liquid mixed pump increases with the increase of gas-water volume ratio in the range of 0.01～0.05 and 0.05～0.30 MPa.At the water temperature of 5.6,13.5 and 30.3°C,the dissolved oxygen concentration in the oxygen-enriched water can reach 46.26,45.71 and 36.95 mg/L,respectively.Increasing the outlet pressure can increase the dissolved oxygen concentration,but when the pressure exceeds0.25 MPa,the dissolved oxygen increment of oxygen-rich water produced by the gas-liquid mixing pump will not increase significantly due to the limitation of oxygen intake.Increasing the gas-water volume ratio can increase the dissolved oxygen concentration,but the oxygen absorption efficiency decreases with the increase of the volume ratio.When the volume ratio is 0.01,the oxygen absorption efficiency is the highest,up to 91%;compared with other aeration equipment,the gas-liquid mixing pump also has the characteristics of low energy consumption.When the water temperature is 30.3°C and the volume ratio is0.01,the lowest power efficiency can reach 22.32 kg O2/（k W·h）.As a pure oxygen mixing device,the gas-liquid mixing pump performs better in both oxygenation capacity and energy saving.（2）According to the test results of the dissolved oxygen performance of the gas-liquid mixing pump,the optimal working parameters were obtained as follows:the gas-water volume ratio was 0.01,the working pressure was 0.25 MPa,and the gas-liquid mixing pump with a power of 3 k W was selected to carry out the aeration test of the captive barrel（diameter 4 m,height 2 m,aquaculture water volume 20 m3）on the pond captive platform.The results showed that in the continuous aeration test,when the average water temperature was 19.3°C,the gas-liquid mixing pump increased oxygen with four captive barrels as a unit.The dissolved oxygen in the captive barrel could reach 11 mg/L during the light time and 9 mg/L at night.The dissolved oxygen in the captive barrel can reach 10 mg/L in the light time and 8.5 mg/L at night.When the average water temperature in summer was 32°C,the gas-liquid mixing pump increased oxygen for four captive barrels,and the dissolved oxygen in the barrel could reach 6 mg/L in the light time and 4 mg/L at night.Under the same working pressure,changing the amount of oxygen inhalation,when the gas water volume ratio is 0.02,the dissolved oxygen illumination time in the four barrels can reach 6mg/L,and the night can reach 5 mg/L;at a gas-water ratio of 0.005,the dissolved oxygen in the four captive barrels can reach 6 mg/L during the day and remain at 3.5 mg/L at night.In the intermittent aeration test in summer,the gas-liquid mixing pump first provided oxygen-enriched water to two caged buckets.When the dissolved oxygen in the bucket reached the saturation level,the aeration was stopped,and then the other two caged buckets were added with oxygen.The change of dissolved oxygen in the bucket during the whole process was measured.The measurement results showed that the dissolved oxygen in the caged bucket reached the actual saturation value of dissolved oxygen in the water within40 min in both light and dark environments.After that,the dissolved oxygen in the caged bucket increased but the increment gradually decreased.After stopping the aeration,the dissolved oxygen in the bucket decreased to the initial dissolved oxygen level of 3 mg/L after 1 hour.At the four data measurement points distributed around the captive barrel,the fluctuation of dissolved oxygen was kept within 0.2 mg/L,and the uniformity of dissolved oxygen was better.The use of gas-liquid mixing pump combined with pure oxygen can effectively improve the dissolved oxygen content in the cage,which can meet the daily oxygen demand of the breeding object.（3）According to the results of 24 h aeration test in captive barrels,it was found that the dissolved oxygen in the barrel always increased first and then decreased.It was speculated that the dissolved oxygen in the water was significantly correlated with light,and the biological photosynthesis in the water released more dissolved oxygen during the day.In the experiment to explore the effect of light on the effect of biological photosynthetic oxygen evolution in water under dark environment,three control groups（water grass,microalgae,microalgae and water grass）were set up.The white light,red light and blue light were used to illuminate under different light intensities,and the changes of dissolved oxygen in water within 12 hours of light irradiation were measured.The results showed that the dissolved oxygen in water increased under white light and red light irradiation.The effect of white light on photosynthesis was the most significant,followed by red light,and blue light had no significant effect,and the oxygen release effect of aquatic plants was better than that of microalgae.With the increase of light intensity,the photosynthetic oxygen release rate of aquatic plants increased.When the light intensity was 5000 Lux,the light compensation point was reached,and the net photosynthetic oxygen release rate was zero.When the light intensity was 12,000 Lux,the light saturation point of water grass was reached,and the maximum net photosynthetic oxygen release rate of water grass was 6.2μmol/（g·h）;Choosing the appropriate light irradiation can make the biological photosynthesis in water release oxygen,so as to achieve the purpose of increasing oxygen.In this paper,aiming at the problem of poor effect of using air to increase oxygen in high-density pond captive mode,it is proved that the new aeration system of gas-liquid mixed pump+pure oxygen can effectively improve the dissolved oxygen in the water in the captive bucket under the high temperature environment in summer.The effect of light on the photosynthesis of aquatic organisms in dark environment was preliminarily explored,and it was proved that the use of LED lights can promote the photosynthesis of aquatic plants to release oxygen.These results can provide a theoretical basis for the research work of new oxygenation technology in modern aquaculture,and provide a reference for exploring more energy-saving and green oxygenation methods. |
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