A MODELING STUDY OF ANAEROBIC BIOFILM SYSTEMS .2. REACTOR MODELING

A rigorous steady-state model of anaerobic biofilm reactors taking int o account acid-base and gas-phase equilibria in the reactor in conjunc tion with detailed chemical equilibria and mass transfer in acetate-ut ilizing methanogenic biofilms is presented. The performances of ideal completely stirred tank reactors (CSTRs) and plug-flow reactors, as we ll as reactors with nonideal hydraulic conditions, are simulated. Decr easing the surface loading rate increases the acetate removal efficien cy, while decreasing the influent pH and increasing the buffering capa city improves the removal efficiency only if the bulk pH of the reacto r shifts toward more optimal values between 6.8 to 7.0. The reactor ca n have negative or positive removal efficiencies depending on the star t-up conditions. The respiration coefficient plays a critical role in determining the minimum influent pH required for reactor recovery afte r failure. Having multiple CSTRs-in-series generally increases the ove rall removal efficiency for the influent conditions investigated. Moni toring of the influent feed quality is critical for plug-flow reactors , because failure of the initial sections of the reactor may cause a c ascading effect that may lead to a rapid reactor failure. (C) 1995 Joh n Wiley and Sons, Inc.