Study On Bubble Property Parameters In The Process Of Dissolved Air Flotation

In recent years,with the rapid development of economy and the improvement of living quality of residents,water pollution is serious increasingly.Solving the problem of water pollution has become the necessary means for recycling water.Dissolved air flotation technology is one of the important methods for sewage treatment,the property of the microbubble is an important parameter,which has an impact on the treatment result of dissolved air flotation technology.In order to study the property of microbubble,the microbubble size measuring device and the gas holdup measuring device were designed in this paper.CCD method was used to measure microbubble size,then using MATLAB software to analyze the captured images to calculate microbubble diameter.The length of sampling window was 7.5 cm,width was 2.5 cm,thickness was 0.6 mm,bending angle was 5 °,it could reduce microbubble coalescence and microbubble overlap problem caused by photographic technique effectively.Conductivity probe method was used to measure gas holdup,the inner diameter of sampling tube was 1 mm,wall thickness was 0.2 mm,bending angle was 45 °,in order to improve the accuracy of measurement,ultrasound device was added to improve the surface property of microbubble and bubble-coalescence cell was added to make microbubble coalescence.The effects of saturator pressure,TX-100 concentration,and pDADMAC concentration in the saturator on microbubble size distribution were investigated in this paper.The results showed that the microbubble size decreased with the increase of the saturator pressure when the pressure was below 0.4 MPa and the change of microbubble size was insignificant when the pressure increased further.The microbubble size decreased with the increase of TX-100 concentration,while pDADMAC had a minimal effect on the microbubble size in the range of 0-5 ppm.For the gas holdup measuring device,the effect of structure parameter of the device itself on the gas holdup were investigated,it was concluded that the best experimental conditions of this device were listed as follows:bending angle of sampling tube was 90°,suction speed was 100 ml/min,sampling tube inner diameter was 1 mm,wall thickness was 0.2 mm.Finally,the gas holdup measuring device was applied in dissolved air flotation cell in this paper,the effect of water inflow rate and reflux ratio on the gas holdup distribution in flotation cell were investigated.The results showed that:(1)when water inflow rate was 1.5m~3/h,the overall gas holdup decreased with the increase of reflux ratio.In the horizontal direction,gas holdup was larger close to the water inflow side and was smaller in the middle area of the cell,which close to the water outflow side was located between the two above.(2)when water inflow rate was 33m/h,in the horizontal direction,gas holdup had small difference.When sampling depth was less than 25cm,gas holdup was larger when the water inflow rate was 1.5 m~3/h,when sampling depth was greater than 25cm,gas holdup was larger when the water inflow rate was 3m~3/h.