Research On Application Of New Throttling Type Micro-nano Bubble Generator In Ozonation Of Biogas Slurry

With the development of economy and the improvement of people's living standards,the discharge of sewage has increased year by year and the concentration of major pollutants in sewage has continued to rise,the situation of sewage treatment has become even more severe.Activated sludge and ozonaion are two among the most commonly used processes in sewage treatment.Aeration is one of the most important parts in these two processes.The aeration efficiency is directly related to the efficiency of sewage treatment.Micro-nano bubble has the characteristics of large specific surface area and slow rising speed,which can greatly increase the efficiency of aeration.However,the existing micro-nano bubble generators have shortcomings such as too large and too complicated,which limits their application in the industrial field.Aiming at the problems,a new design of micro-nano bubble generator was proposed,which eliminates the high-pressure air pump and the dissolving-air tank and reduces the difficulty of operation.Subsequently,the aeration performance of the micro-nano bubble generator was tested by changing the orifice diameter and the gas-liquid ratio.The preliminary experiment results show that due to the large amount of gas that could not be dissolved in the water,the aeration performance of the device deteriorates when the gas-liquid ratio is too high.According to this,the device was improved by adding a gas-liquid separation tank,which also improves the performance of the generator and makes it a lot easier to operate.The aeration performance of the improved device first increases and then decreases with the increase of the orifice diameter,and increases with the increase of the gas-liquid ratio.But when the gas-liquid ratio comes to 12%,the device malfunctioned.The device achieves the best aeration performance when the orifice diameter is 4.5mm and the gas-liquid ratio is 10%,and the corresponding pressure is0.24MPa.On that situation,the standard oxygen volume mass transfer coefficient of the device is 0.212min^-1,and the oxygenation capacity is 0.00584kg/h,the oxygen utilization rate is 17.7%,and the average diameter of the generated micro-nano bubbles is 38?m.The gas-liquid separation tank can obviously improve the performance of the micro-nano bubble generator,and at the same time curb the performance deterioration caused by the high gas-liquid ratio.When the orifice diameter is 4.5mm and the gas-liquid ratio is 10%,the standard oxygen mass transfer coefficient,oxygenation capacity,and oxygen utilization rate before and after the improvement are 0.123 min^-1,0.00339kg/h,10.2%,and 0.212min^-1,0.00584 kg/h,17.7%,the aeration performance of the latter is 1.72 times that of the former,and the average diameter of micro-nano bubbles is 88?m and 38?m.The efficiency of micro-nano bubble ozonation treatment of anaerobic fermentation biogas slurry is affected by the ozone flow rate,and there is an optimal reaction time.The best working conditions of the process are when the ozone flow rate is 40 L/h and the reaction time is 90 minutes.On that situation,the COD removal rate is 35.5%,the chroma removal rate is 45.9%,and the BOD₅/COD ratio is 26.2%.Micro-nano bubble generator can effectively improve the performance of ozonation.When the ozone flow rate is 40 L/h and the reaction time is 90 minutes,the COD removal rate,BOD₅/COD ratio and chroma removal rate of the micro-nano bubble aeration experiment group are 1.6 times,1.4 times and 2.1 times of the experiment group that uses Gravel generator,meanwhile,the average COD removal cost is only 71.5%.