Oxygen transfer in circular surface aeration tanks

Abstract

Surface aeration systems employed in activated sludge plants are the most energy-intensive units of the plants and typically account for a higher percentage of the treatment facility's total energy use. The geometry of the aeration tank imparts a major effect on the system efficiency. It is said that at optimal geometric conditions, systems exhibits the maximum efficiency. Thus the quantification of the optimal geometric conditions in surface aeration tanks is needed. Optimal geometric conditions are also needed to scale up the laboratory result to the field installation. In the present work, experimental studies have been carried out on baffled and unbaffled circular surface aeration tanks to ascertain the optimal geometric conditions. It is found that no optimal geometric conditions exist for the liquid/water depth in circular surface aeration tanks; however, for design purposes, a standard value has been assumed. Based on the optimal geometric conditions, a scale-up equation has been developed for the baffled circular surface aeration tanks.

Power characteristics of surface aerators

“…The power number increases with increase in number of baffles, which can be explained by the increase in resistance offered by the increasing number of baffles. In oxygen transfer experiments four baffles were found to be optimal, so in further experiments four baffles were used 27…”

“…Rao and Kumar35 have shown that theoretical power per unit volume X ( = F 4/3 R 1/3 ) represents the small‐scale energy dissipation which occurs surrounding the impeller. This parameter was found useful in simulating the oxygen transfer rates of baffled and unbaffled surface aeration systems3, 27, 34, 36 The same parameter X may also be considered for simulating the power characteristics of baffled surface aerators.…”

Mass transfer and shear rate in baffled surface aerator

“…The Rushton turbine produces radial flow and high shear rates near the impeller, which is important for air dispersion. Conditions of geometric similarity, i.e., √A/d=2.88, 24 and h/d=0.94, as suggested by Rao and Jyothish [20] were maintained in all the surface aerators.…”

Evaluation and Optimization of Efficiency and Mixing Time in a Surface Aeration Tank

“…As excess treatment obligations are imposed, considerations for energy demand and conservations also increases through wastewater treatment plants (WWTPs). Furthermore, it has been estimated that the aeration process consumes more than half of the whole power requirements in WWTPs [3]. Therefore, increase of the gas-liquid oxygen transfer is considerably favorable for convenient energy utilization in wastewater treatment processes [4], [5].…”

“…However, surface aerators are more popular due to their ease of operation and comparative efficiency [3], [6]. Surface aerators are extensively used for the treatment of wastewater by biological oxidation.…”