B.S. Magbanua Jr. (USA)
Simulation; Waste Processing; Wastewater Treatment; Process Uncertainty; Stochastic Modeling
Probabilistic modeling of activated sludge wastewater treatment systems was performed to compare the uncertainty, with respect to attaining pollutant removal targets, associated with specific reactor configurations (conventional, completely mixed, and step feed activated sludge systems) and operating variables (solids residence time, hydraulic residence time, recycle ratio, and influent distribution). Stochastic simulation results showed that different reactor configurations inherently had different levels of uncertainty associated with them. Whether a specific operating parameter had an effect on uncertainty, and the extent of that effect, was dependent on the process configuration. In all of the configurations considered, process uncertainty could be reduced by increasing the solids residence time. Treatment uncertainty was also reduced when the hydraulic regime of the reactor was closer in character to plug flow rather than to completely mixed. Hence, the treatment uncertainty for the conventional activated sludge system was lower than that for the completely mixed activated sludge system. Furthermore, operational changes that enhanced mixing, such as increasing the recycle ratio in a conventional activated sludge system, or distributing the influent along the length of the reactor basin in a step feed activated sludge system, also tended to increase process uncertainty. In every case, system response could be traced to the effect of the imposed configuration and parameter changes on the hydraulic regime and reaction kinetics within the treatment system.
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