Modeling and optimization of biological sequential batch reactors

This work deals with modeling and operation optimization of biological sequential batch reactors (SBR). The SBR is a fill-and-draw biological sludge system for wastewater treatment. In this system, wastewater is added to a single batch reactor, treated to remove undesirable components, and then, discharged. In this paper, a global model of a gas-solid-liquid SBR is presented to investigate and optimize operational strategies. The model can address the differences between aerated and anaerobic systems by assigning adequate parameter values related to the aeration and reaction systems. Fluctuating operation conditions during cycles such as disturbances in the organic loading rate, stirring rate and cycle time, result in strong numerical discontinuities that can be included in the simulation schedules. An existing set of experimental data is used to show a model application based on an anaerobic SBR. A good agreement was obtained between experimental and predicted values. Optimization results are based on minimizing the reaction time/total cycle time ratio subjected to path pH constraints and interiorand end-point constraints related to the pollutant removal efficiency and settling conditions. A decrease of 22% in the total cycle time, i.e. an increase in the organic loading rate from 787 to 985 mg dm d is reached without modifying the quality of effluent.