Abstract
The removal of Cd, Cr, Cu, Pb, Ni, and Zn in an activated sludge pilot plant acclimatized to nitrilotriacetic acid (NTA) has been compared with an identically operated plant receiving no NTA. During steady-state operation the removal of Pb and Ni was reduced in the presence of NTA but there was no detectable difference in mixed liquor metal concentrations. Transient changes in the influent metal concentration of an order of magnitude had only a slight influence on NTA removal; Ni had the greatest effect, Cd and Cu some effect and Pb a negligible effect. Short term variations in influent NTA concentrations had no effect on NTA removal. A transient increase in influent NTA concentration caused a slight decrease in NTA removal. Transient increases in influent Ni concentration combined with reductions in temperature to 10 and 7.5 °C had a slight adverse effect on NTA removal. This effect did not appear to be additive or synergistic. Combinations of transient increases in influent NTA concentration and reductions in temperature caused a significant decrease in NTA removal. The effect was synergistic rather than additive.
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