Nitrification Studies at Non-limiting Substrate Concentrations

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Theoretical models of nitrification were tested using an experimental model consisting of a column of glass beads inoculated with nitrifying bacteria, through which was passed a constant flow of substrate at non-limiting concentration. Effluent was analysed for conversion products. Both zero-order and first-order rate constants for substrate conversion decreased by 1·4% for each 1 ml h−1 decrease in flow rate presumably because of the development of oxygen limitation. Logistic growth kinetics described growth adequately and bacteria were distributed evenly throughout the column after establishment of steady states. Bacterial concentrations of 1·4 × 109 ml−1 and conversion rates of 5·62 × 10−9 p.p.m. N as NO2 − h−1 organism−1 were obtained for Nitrobacter and 6·47 × 106 ml−1 and 3·75 × 10−7 p.p.m. N as NH4 + h−1 organism−1 for Nitrosomonas. During periods of oxygen starvation a lag was observed following increases in flow rate producing undershoots in product concentrations before establishment of new steady states.