Modeling and Simulation of Anaerobic Wastewater Treatment and Its Application to Control Design: Case Whey

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Abstract
Modeling and simulation of the anaerobic treatment of whey wastewater was studied. A model inpluding five groups of organisms, whey substrate, butyric, propionic, and acetic acids, CO2, H2, and CH4, was developed for single‐ and two‐stage anaerobic fluidized bed reactors. It included thermodynamic limitations for the acetogenesis reaction, acid‐base equilibria of dissociating compounds (organic acids and CO2) for variable and constant pH situations, gas‐liquid phase mass transfer, and measurement dynamics. The model was adequate to describe both the steady‐state and dynamic behavior of the reactors and was used to study various control schemes. In all cases the feed flow rate was the manipulated variable. Controls of pH, dissolved hydrogen, and organic acids were all successful in simulation and experiment. Simulations were used to determine optimal control parameters for conventional proportional—integral (PI) or proportional—integral—differential (PID) control. The experimentally found optimal values were in close agreement with predetermined simulated values. Simple control using gas analysis results did not give stable control, either in the simulation or in the experiment.