Comparative evaluation of mass transfer of oxygen in three activated sludge processes operating under uniform conditions

This investigation was conducted in three laboratory-scale activated sludge processes, namely, the conventional completely mixed activated sludge process (CMAS), the modified Ludzack-Ettinger process (MLE), and the University of Cape Town (UCT) process. These systems were operated under controlled conditions by feeding a uniform influent at a single 10-d solids retention time (SRT). The oxygen transfer parameters (K_La_f, α, OTR_f, and OTE_f) determined indicated that the alpha (α) and oxygen transfer efficiency (OTE_f) in processes where the enhanced biological phosphorus removal (EBPR) mechanism was active were higher than in the conventional completely mixed activated sludge (CMAS) process, where such a mechanism was absent. Thus, presenting a clear evidence of improved oxygen utilization in activated sludge processes containing unaerated, anoxic, and anaerobic selector zones. Key words: biological nutrient removal, completely mixed activated sludge process, oxygen uptake rate, oxygen transfer efficiency.