THE INFLUENCE OF SUPERFICIAL VELOCITY AND BUBBLE HOLD-UP IN A VERTICAL AERATOR COLUMN TO THE OXYGEN TRANSFER COEFFICIENT

Abstract

To optimize aeration process in a waste water treatment aeration tank, numerical model analyses can be utilized. However, it is necessary to understand the dynamics of air bubble flow within the aeration tank and the oxygen mass transfer from within bubbles to the body of water or waste water. A research for obtaining the relationship between the oxygen mass transfer and the bubble concentration and size has been conducted. Before conducting some experiments involving bubble flow dynamics and oxygen mass transfer measurements, some previous research results on the related subjects was elaborated. Two conditions were considered, those are the bubble flow dynamics and oxygen mass transfer within plain water and within water with artificial sludge. The measurements were done in a two milimeter thick glass walled aerator column of 95 x 95 x 300 mm size. Spargers for air injection were placed on the bottom of the aerator column. Air compressor was used in order to push the air into the bottom of the aerator column. For measuring the discharge of the air flow a rotta meter was installed between the air compressor and the spargers. The bubble dinamics was observed using digital image analyses by a video camera, computers and video capture and image analysis softwares. The oxygen mass transfer was measured through the change of Natrium Sulfide concentration that was added into the water. Cobalt was used as catalist for speeding up the reaction process so that the reaction proses was not controlling the rate of the whole sequence of mass transfer and reaction processes. The result of the research indicates that the individual bubble size remains constant between 3.4 and 3.7 mm within the superficial velocity variation range of between 0.09 and 0.19 cm/s. Furthermore, for any value of superficial velocity, the presence of the artificial sludge increasing the bubble concentration or bubble hold-up. The oxygen mass transfer coefficient appears to be positively influenced by the superficial velocity.