The relationship between dissimilatory nitrate reduction and oxygen uptake by cells of an Alcaligenes strain in flocs and in suspension and by activated sludge flocs

Abstract

The oxygen uptake and the dissimilatory nitrate reduction by anaerobically grown cells of a denitrifying Alcaligenes strain, occurring in floc form or in suspension, were studied at different oxygen concentrations in the surrounding medium. When the oxygen concentration in the medium fell below 1·5 mg l −1, the nitrate reduction by the cells within flocs increased considerably. The cells in suspension showed an increased nitrate reduction when the oxygen concentration was below 0·1 mg l −1. When anaerobically grown cells had been aerated for 24 h in a nitrogen-free medium, the cells became sensitive to respiration inhibition by nitric oxide, resulting from nitrate reduction. This gave rise to an increased nitrate reduction below 2·5 mg oxygen l −1 when the cells were aggregated in flocs and below 0·1 mg oxygen per litre when the cells were in suspension. The nitrate reduction by the denitrifying, floc-forming pure culture was compared with that of activated sludge flocs.