The validity of the TTC-test for dehydrogenase activity of activated sludges in the presence of chemical inhibitors.

Dehydrogenase activity of activated sludges coming from a laboratory plant, has been evaluated by the TTC-test in the presence of some chemical toxics. The results obtained have shown that, for all inhibitors tested, there exists a range of concentrations in which the dose-response relationship is linear. As far as the comparison of the inhibition data from the TTC-test and from the Oxygen-respiration rate is concerned, the results obtained show that the inhibitors tested may be divided into three groups: (i) inhibitors which inhibit the Oxygen-respiration rate more than th Dehydrogenase activity (Zn2+, Cd2+, Ni2+, Hg2+, Zn(CN)4(2-), Cd(CN)4(2-)); (II) inhibitors for which there are no significant differences in the inhibition value obtained by the two methods (CN-, C6H5O-, C6Cl5O-, C6H3ClO-, Hg(CN)4(2-)); (iii) inhibitors which inhibit the dehydrogenase activity more than theoxygen-respiration rate (Cu2+, CrO4(2-), Ni(CN)4(2-)). The inhibition data obtained by other authors evaluating by direct methods (COD reduction, turbidity of the final effluent etc.) the performance of pilot or laboratory plants in the presence of some of the toxics used in the present research, are in sufficient agreement with the dehydrogenase inhibition data obtained in this work.