Effects of trace levels of copper, chromium, and zinc ions on the performance of activated sludge

The effects of copper, chromium, and zinc ions, at trace levels, on the per formance of a simulated activated sludge process were investigated. The res ults of batch adsorption experiments showed that the adsorption of copper, chromium, and zinc ions followed both the Langmuir and Freundlich isotherms . The presence of trace levels of these three metals not only reduced the a dsorption rate of organic matters but also the chemical oxygen demand adsor ption capacity (CAC) of the activated sludge. Metal ions competed with ale organic substrate for adsorption binding sites on the surfaces of activated sludge bioflocs and reduced the CAC. Studies performed in a sequential bat ch reactor (SBR) showed that the presence of trace levels of heavy metal io ns in wastewater affected the SBR performance to different extents dependin g on the hydraulic retention time (HRT). When the reactors were operated at short HRTs of 2.5 d or less, the presence of trace levels of heavy metal i ons reduced substantially the CAC of activated sludge, which, in turn, affe cted significantly the performance of the SBR. However, under longer HRTs ( e.g., 5 d), the heavy metal ions in the wastewater reduced the CAC but had no significant effect on the chemical oxygen demand removal efficiency.