Laboratory-scale activated sludge treatment systems were operated under dynamic loading conditions to investigate the non-steady state behaviour of heavy metal contaminants under controlled conditions. Four step tests were conducted in which an incremental increase in the concentrations of selected contaminants was applied to the reactor feed from background levels of about 100 µg/L to levels of about 1000 µg/L for each metal over a period of approximately three hydraulic retention times. Effluent metal concentrations rose significantly to levels of approximately 500 µg/L. They remained elevated for long periods after termination of the metal perturbations. Solids retention time (SRI) did not appear to influence metal removal efficiency over the range tested. Hydraulic retention time (HRT) effects were difficult to discern from the confounding effect of influent metal concentration.

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