OXYGEN TRANSFER BY MECHANICAL AERATION

Abstract

Aeration is a process of bringing the water in intimate contact with air. While doing so the water absorbs oxygen from the air. Thus, dissolved oxygen level increases in the water. The dissolved oxygen helps aerobic bacterial decompo- sition of organic wastes as well as direct oxidation of certain metals. It also helps in removing bad odour and taste by oxidising and precipitating certain dissolved gases and compounds in the water. Oxygen transfer by mechanical aeration has been found simpler, economical, easy to adopt method as compared to many other conventional methods used so far like bubble aeration, trickling beds, spray nozzles and cascades. In the present stydy, experiments were carried out to assess the effect of turbulence on the dissolved oxygen (D.O.) of the water. The intensity of turbu- lence is varied by varying impeller speed, number of blades on the plate and submergence of the impeller. Further, a recent concept of overall oxygen transfer coefficient (KLa) has been employed in analysing the experimental results to avoid certain inaccuracies and assumptions. The experimental results show that at the upper zone the increase in KLa decreases with increase in submergence at a faster rate of the impeller. With increase in speed, turbulence increases proportionately and there is always increae in KLa with increase in impeller speed. As number of blades increases from 4 to 8 the turbulence changes and is found to be maximum in case of 8 bladed plate and hence increased aeration