Operating the activated sludge process to decrease cell yield without increasing oxygen consumption

The objective of this study was to demonstrate that cell yield in activated sludge processes can be decreased without increasing oxygen consumption by applying operating conditions that encourage "futile cycling". During futile cycling, compounds are synthesized and catabolized by the microbial culture without a corresponding change in cell mass.;In this study, laboratory-scale activated sludge reactors were used and operated as sequencing batch processes. As part of the experimental program conducted, the performance of these reactors were monitored as their operation was changed from normal to intermittent operating conditions. Under normal operation, the reactors were fed once and aerated uniformly during the react step. Under intermittent operation, the reactors were either fed or aerated intermittently during the react step to induce "futile cycling".;During intermittent feeding, cell yield decreased by 24 percent and oxygen consumption decreased by 18 percent, on the average. During intermittent aeration, cell yield decreased by 23 percent and oxygen consumption increased by 4 percent, on the average.;Intermittent feeding and intermittent aeration operating schemes may be applied to full-scale systems using sequencing batch operation or to continuous-flow processes using a modified configuration of tapered aeration, step aeration, or contact stabilization. The results anticipated are reductions in both cell yield and oxygen consumption greater than were demonstrated using laboratory-scale reactors.;The two major operating expenses for an activated sludge wastewater treatment facility are associated with sludge handling and aeration. Sludge handling requirements are affected by cell yield and aeration requirements are affected by oxygen consumption, defined as the mass of oxygen consumed per mass of substrate utilized. By operating the activated sludge process such that cell yield decreases without increasing oxygen consumption, significant reductions in the operating costs for an activated sludge wastewater treatment facility may be realized.