MODELLING OF OXYGEN TRANSFER IN DEEP DIFFUSED-AERATION TANKS AND COMPARISON WITH FULL-SCALE PLANT DATA

Abstract

In upgrading or extending activated sludge treatment plants, there is a trend to apply deeper (8 to 12 m) aeration tanks than until now (4 to 6 m). Such tanks consume less area, need less air and produce less off-gas. Sometimes, a greater aeration efficiency (kg O2/kWh) and hence energy savings are expected. On the other hand, there is not sufficient experience to safely design air diffusion systems for deep tanks. Based on the physics of gas transfer, a model for simulation of oxygen transfer in deep tanks is developed. The simulated data allow quantitative conclusions with respect to the potential advantages stated above. According to the model, a reduction of the required air flow is considerable up to depth of some 15 m but energy savings cannot be expected. The model is verified using 98 full-scale plant measurements at various tank depths. The comparison shows a good agreement between simulated and actual data. Further investigations are required to support the model at greater depth and to enable a safe design procedure for air diffusion systems in deep tanks.