Experimental Investigation On Oily Water Treatment By Counterflow Flocculation Flotation Technology

Flotation method is a high effective way in solid-liquid or liquid-liquid separation field. By the generalization of the current developments and application status of flotation technology, especially dissolved air flotation technology, a novel type of counterflow flocculation flotation device was proposed based on the recent developments of flotation theories and experimental study was deeply conducted on its performance on oily water treatment. .The cylindrical flotation device adopts vertical current mode, in which bubbles and flocci moves and contacts reversely. Bubbles-flocci aggregation is formed when bubbles and flocci collides and are adhered to each other. The froth ascents and is removed from froth outlet automaticly. Dissolving tank is used in the air-dissolving system. Air-dissolving water is formed in the tank from compressed air and water and then is released by a throttle valve.The interaction of micro-bubbles and flocci were determining factors on the efficiency of the flotation method. The properties and interaction of the bubbles and flocci and the mechanism of motion of the bubble/flocci aggregation were analyzed in this paper. The optimal operating conditions were determined by the experimental analysis on parameters as the amount of air released and the diameter of micro-bubbles. From the experiments it was found that that the diameters of most of the bubbles produced by the air-dissolving system can meet the requirements of flotation process when the pressure of the system was between 0.28~0.30MPa and the water inflow of the air-dissolving tank was 160L/h.The counterflow flocculation flotation system was developed in this paper and its performance on oily water treatment was studied by experiments using oily water prepared by the author. Tap water, diesel oil and emulsifier were used in wastewater preparation and the oil content of the water was between 150mg/L and 200mg/L. The coagulants used in this paper were PAC and PAM. Experiments verified the existence of the bubble-flocci aggregation blanket in the column, which played an important role in the water treatment process. The influencing factors including the amount of water treated, the dissolving pressure, the reflux ratio of air saturation system, the height of the reacting region, the amount of coagulant used and the pH value of wastewater were studied. The operating parameters obtained from those experiments were as follows: the favorable concentration of PAC and PAM used were 50mg/L and 1mg/L separately; the operation pressure was 0.3MPa; the optimal recycle ratio was 70%; the flowrate of the wastewater should be kept between 200L and 400L to guarantee a satisfactory quality of water output and the pH value of raw water should be 6~8. The experiments on in situ oily water from Shengli Oilfield were also conducted in this paper under the optimal conditions determined in the above experiments while the amount of PAC used was varied. The result shows that the de-oiling rate can attain to 79.5% when the concentration of PAC was 40mg/L.Experiments showed that the oily water can be treated effectively by counterflow flocculation flotation column and it occupied comparatively less area and was an energy-saving device.