Effects of growth rate and influent substrate concentration on effluent quality from chemostats containing bacteria in pure and mixed culture

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Abstract
Studies were performed using pure cultures of A. acrogenes and E. coli and a heterogeneous microbial population growing in carbon‐limited chemostats with glucose as the sole carbon and energy source. A two‐level factorial experimental design was employed to test the hypothesis that the concentration of growth‐limiting substrate in a chemostat is controlled by the growth rate alone and is independent of the concentration of substrate entering the reactor. The pure culture experiments showed that the conclusions depend upon the measurement employed for growth‐limiting substrate. When the concentration of glucose was measured directly, the hypothesis was found to be true within the limits of the study (500–1500 mg/liter). However, if the chemical oxygen demand (COD) test was used as the measure of growth‐limiting substrate the hypothesis was found to be false. When heterogeneous cultures were employed the hypothesis was false regardless of the technique used to measure the concentration of growth‐limiting substrate. Nevertheless, it was possible to generate regression equations which described the interactions among influent COD, growth rate, and effluent COD with a high level of correlation.