Cadmium uptake by activated sludge in a semicontinuous system

The influence of solid retention time on cadmium uptake by activated sludge at different concentrations of the metal was studied. Activated sludge was cultivated in a lab-scale bioreactor with plug-flow pattern. Respirometric measurements were applied to evaluate the inhibitive effects of cadmium on activated sludge. The obtained values of the conditional adsorption constant indicate a similar affnity of cadmium to activated sludges cultivated in both plug-flow and complete-mixing reactors. The decrease of the metal affinity to activated sludge cultivated in a semicontinuous system with an increasing solid retention time was observed. High value of the mass ratio of cadmium in the activated sludge to metal in the surrounding liquid phase at equilibrium conditions made possible subsequent cadmium recovery. Maximum inhibition of cadmium to non-acclimated activated sludge was observed after 6 to 10 hours of exposure. The highest toxicity of this metal was observed between 2 and 5 hours after cadmium dosing of the acclimated sludge. A beneficial influence of solid retention time on the toxicity of the metal with regard to non-acclimated activated sludge resulted from this work.