SummaryThe kinetic behavior of heterogeneous microbial populations of sewage origin was studied in a single-stage isothermal continuous flow completely mixed aeration tank. A series of experiments were carried out a t various dilution rates using glucose as the growth limiting substrate. The steady-state behavior of the system was observed at each dilution rate and the results were found to fit fairly well with the steady-state equation based on the Monod model with anThe growth kinetics of cells harvested at steady state for each dilution rate were studied using batch experiments. The multiple response data of the system as functions of time were used to estimate the parameter values in the above kinetic model. It was found that values of the growth parameters changed significantly and systematically with cell population. For example, values of p, were high a t high dilution rates and low a t low dilution rates. It was also found that only those batch growth parameters from cells obtained a t fairly high dilution rates are comparable with those estimated by the results of steady-state operations. The results of this investigation suggest that 1) different cell populations predominated at different steady-state dilution rates, with high dilution rates resulting in predominantly fast-growing organisms and low dilution rates resulting in predominantly slow-growing cells, and 2 ) risk exists in any randomly picked batch experiment to predict the steady-state behavior of the system when heterogeneous microbial populations must be used.

SummaryThe kinetic behavior of heterogeneous microbial populations of sewage origin was studied in a single-stage, isothermal, continuous flow, completely mixed aeration tank. A series of experiments were carried out a t various dilutions rates using glucose as the limiting substrate. The cell dry weight and substrate concentration in terms of chemical oxygen demand (COD) were continuously monitored. The results indicate that reproducible steady-state conditions can generally be obtained; however, multiple steady states were observed at dilution rates near washout. At low dilution rates (below about 0.1 hr-l) the contribution of microorganism decay became appreciable. Using the multiresponse data of cell dry weight and COD, the parameter values in various existing growth models were estimated. The analyses of variance and residuals revealed that models proposed by Moser, Monod, and Contois, each with a decay term added, were significantly better than the other models which were tested.

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