Evaluation of steady‐state‐biofilm kinetics

Laboratory‐scale biofilm reactors were used to evaluate a model of the kinetics of steady‐state biofilm and the concept that there is a minimum concentration, S_min, below which no steady‐state activity can occur. With acetate as the ratelimiting substrate, the steady‐state concept of S_min was verified for naturally grown biofilms. Substrate removal and biofilm thickness declined rapidly as the substrate concentration approached S_min, which was 0.66 mg/liter for acetate. Using independently derived kinetic parameters, the model of steady‐state‐biofilm kinetics successfully predicted substrate utilization and biofilm thickness without the need for fitting factors. The results imply that organic materials may persist in water and wastewater, in part, because they are too low in concentration to supply sufficient energy to sustain the microorganisms.