Response of sOUR and AUR to heavy metal contamination in activated sludge

The aim of this work was to make a contribution to the knowledge of inhibit ion by heavy metals of both nitrifying and heterotrophic bacteria in the ac tivated sludge, based on measurements of ammonium uptake rats (AUR) and oxy gen uptake rate (sOUR) activities. For the inhibition tests, we used differ ent concentrations of the following heavy metals: Cd2+, Cr6+, Cu2+, Pb2+ an d Zn2+, and the toxic effect of each metal was measured after 1 and 24 h ex posure. Tests were performed on activated sludges from a full-scale nitrify ing plant. The inhibitory concentrations were evaluated for each ion and in a decreasing order of toxicity two groups were found: Cd > Cu > Zn and Pb > Cr. Nevertheless, experimental results indicated that the response of AUR and sOUR to the tested metals was different. Higher AUR values than sOUR o nes were observed in the tests with Cd2+, Cu2+ and Pb2+ indicating a lower sensitivity of nitrifiers to these heavy metals in comparison with heterotr ophs. Inhibitory effects of Cr6+ and Zn2+, were quite similar on both AUR a nd sOUR activity. Our results suggest that in nitrifying activated sludge p lants the sOUR test can be used better than AUR test to identify possible i nhibitory effects of heavy metals from wastewater. (C) 1999 Elsevier Scienc e Ltd. All rights reserved.