Quantification of energy and cost reduction from decreasing dissolved oxygen levels in full-scale WRRFs.

Aeration systems often lack the efficiency to maintain a desired residual dissolved oxygen (DO) concentration in the tank in part because little consideration is given to the dynamic daily and seasonal loading conditions. Although advanced aeration controllers exist, the majority of plants have DO set points typically based on common practice and literature values rather than site-specific conditions, which can result in DO set points higher than those necessary to meet treatment objectives. DO set point reduction strategies have primarily been proposed through either static or dynamic simulations. In this study, the substantial improvements associated with DO set point reduction are demonstrated at full scale. A yearlong characterization of full-scale aeration dynamics captured the effect of diurnal and seasonal fluctuations on oxygen transfer and energy demand, and so facilitated the estimation of the potential savings of DO reduction strategies. Full-scale validation provided direct evidence of DO reduction strategies inducing an overall enhancement of oxygen transfer efficiency along the different bioreactors, while confirming that energy savings as high as 20% were feasible. This study quantifies the influence of oxygen transfer efficiency on operating choices and site-specific conditions (control strategy, loading conditions, influent flow variability, etc.).