ESTIMATING OXYGEN TRANSFER KLa, SOTE AND AIR FLOW REQUIREMENTS IN FINE BUBBLE DIFFUSED AIR SYSTEMS

Oxygen demand in aerated activated sludge reactors varies with time, necessitating a varying oxygen supply rate to maintain a desired dissolved oxygen (DO) concentration. This paper demonstrates how diffuser performance in fine bubble aeration systems can be modeled, accounting for diffuser density, and changing SOTE with air flow per diffuser. The peaks and minimums in different zones of an activated sludge system usually will not be coincident, so it is difficult to accurately estimate total air requirements, as well as time-varying requirements. The approach in this paper overcomes these problems through quantifying (1) the change in oxygen mass transfer coefficient (KLa) with changing air flow in each zone, and (2) accounting for different diffuser densities. If this modeling approach is incorporated in a process simulator that quantifies time-and-space variations in oxygen demand, then accurate estimates of time-varying air supply in different zones can be estimated, and hence more realistic estimates of total air supply needs. Also, it allows a comprehensive analysis of the interaction between diffuser density and oxygen transfer efficiency for the optimal design of aeration systems.