MODELING AND SIMULATION OF ANAEROBIC WASTE-WATER TREATMENT AND ITS APPLICATION TO CONTROL DESIGN - CASE WHEY

Modeling and simulation of the anaerobic treatment of whey wastewater was studied. A model including five groups of organisms, whey substrat e, butyric, propionic, and acetic acids, CO2, H-2, and CH4, was develo ped for single- and two-stage anaerobic fluidized bed reactors. It inc luded thermodynamic limitations for the acetogenesis reaction, acid-ba se equilibria of dissociating compounds (organic acids and CO2) for va riable and constant pH situations, gas-liquid phase mass transfer, and measurement dynamics. The model was adequate to describe both the ste ady-state and dynamic behavior of the reactors and was used to study v arious control schemes. In all cases the feed flow rate was the manipu lated variable. Controls of pH, dissolved hydrogen, and organic acids were all successful in simulation and experiment. Simulations were use d to determine optimal control parameters for conventional proportiona l-integral (PI) or proportional-integral-differential (PID) control. T he experimentally found optimal values were in close agreement with pr edetermined simulated values. Simple control using gas analysis result s did not give stable control, either in the simulation or in the expe riment.