The influence of different substrates on the oxygen uptake rate (OUR) of sludge composed of heterotrophic and autotrophic bacteria was determined, in order to characterize the most suitable substrate for aerobic respirometric tests was the object of this research. Four different sludges were used, generated in variants of activated sludge systems. The OUR of the heterotrophic and autotrophic (nitrifying) bacteria was determined after additions of the different tested substrates by the technique of open semi-continuous aerobic respirometry, described in Van Haandel and Catunda (1982). An automated respirometer coupled to a computer was used in all respirometric tests. The OUR of the heterotrophic organisms, substrates was determined after adding separately sodium acetate (C2H3NaO2), ethyl acetate (C4H8O2), ethanol (C2H6O), glucose (C6H12O6) and phenol (C6H6O). For the autotrophic nitrifying group ammonium bicarbonate (NH4HCO3), ammonium chloride (NH4Cl) and sodium nitrite (NaNO2) were used as substrates. The results of the tests with the heterotrophic group of bacteria showed that significant differences in the OUR and hence in the metabolic rate by these organisms when the selected substrates were used, with sodium acetate exerting the highest OUR. For the group of nitrifying bacteria ammonium bicarbonate was the most appropriate substrate. The tendency of highest biodegradability and substrate affinity for sodium acetate and ammonium bicarbonate was observed for all four sludges from the different systems that were used in the investigation.
aerobic respirometry; substrates; activated sludge
