Shock Effects of Copper Ion on Activated Sludge Unacclimated and Its Recovery Technique

Abstract

To study the effects of heavy metals on the pilot-scale activated sludge process, the uptake of heavy metals and the removal rate of COD Mn by activated sludge were investigated in various conditions. When 20 mg/L of copper ion was added to the sequence batch reactor (SBR) of the unacclimated activated sludge, copper ion was rapidly adsorbed by the activated sludge flocs at first and then released from them after aeration. The copper ion concentration of mixed liquor in the reactor increased until the removal rate of COD Mn became constant. When three kinds of the additives including special nutrients (as COD Mn 45 mg/L), powdered activated carbon (PAC, 50 mg/L) and condensed sludge (as MLSS less than 300 mg/L), which are possible candidates for the recovery techniques, were added to the activated sludge, different bio-kinetic constants were obtained, indicating different inhibition rates of treatment efficiency. In the case of special nutrients, the removal rate of COD Mn was the highest among all three additives, showing that they stimulated microorganisms in the activated sludge to absorb organic substances. Addition of PAC and condensed sludge also improved the removal rates of COD Mn and copper ion. Especially when the organic load was light, the addition of PAC could efficiently remove organic substances and copper ion from the mixed liquor. However, the addition of the condensed sludge increased the turbidity of the mixed liquor. And some long time aeration was found leading to the deflocculation of activated sludge.