Einfluß von Nitrilotriessigsäure auf die Sorption von Schwermetallen an definierten Feststoffphasen (Calcit, Illit, Montmorillonit, Algenzellwände)

In order to estimate the possible influences of Nitrilotriacetic Acid (NTA)on the sorption of metals in sewage treatment plants and in surface waters laboratory experiments were performed using defined mineral phases (Calcite, Illite, Monmorillonite) and an organic substrate consisting of cell walls of the algae Scenedesmus quadricauda. The application of algal cell walls for the first time enabled the quantitative recovery and analysis of the organic solid matter in such experiments. The complexation reactions implying organic components are strongly pH-dependent; for lead and copper the decrease of sorption is strongest at lower pH-values (pH 4 and 6), whereas for cadmium and zinc this effect is more evident in the experimental series at pH 8. Assuming a NTA-concentration of 3 mg/l in the effluents of sewage treatment plants the sorption of zinc should be reduced to about the half, of cadmium from approx. 20% to 5%, compared to NTA-free conditions. In surface waters - at NTA-concentrations about one order of magnitude smaller than in sewer systems - the sorption rate of zinc should be lowered significantly as well, whereas the sorption of cadmium would be affected to a lesser extent. Additional experiments will be performed to clarify the question, to what extent the complexation reactions with NTA in the sewage systems are affecting the interactions of metals and solid matter in the receiving surface waters.

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Einfluß von Nitrilotriessigsäure auf die Sorption von Schwermetallen an definierten Feststoffphasen (Calcit, Illit, Montmorillonit, Algenzellwände)