Monitoring (60)Co activity for the characterization of the sorption process of Co(2+) ions in municipal activated sludge

In large volumes produced activated sludges from wastewater treatment plants (WWTPs) with low concentrations of heavy metals can be utilized as agricultural fertilizers and soil conditioners. Increased contents of toxic xenobiotics are limiting factors that affect the utilization of these heterogeneous wastes. The main aim of our paper was to show the utilization of dried activated sludge (DAS) from municipal WWTP as potential Co(2+) ions sorbent i.e. for non-agricultural purposes. The radio indicator method by radionuclide (60)Co and γ-spectrometry for characterization DAS sorption properties was used. DAS soluble and solid fractions were characterized by biochemical, ETAAS and CEC analysis. The sorption of Co(2+) ions by DAS was rapid process and equilibrium was reached within 2 h. Sorption capacity of DAS (Q) increased with the initial concentration of CoCl(2) in the range from 100 to 4,000 μmol l(−1), reaching 20 and 160 μmol g(−1). Obtained Q values were depent on pH value from 2.0 to 8.0. The maximum sorption capacity (Q (max)) of DAS at pH 6 calculated from mathematical model of Langmuir adsorption isotherm was 175 ± 9 μmol g(−1). FT-IR analyses showed the crucial role of carboxyl functional groups of DAS surfaces on cobalt uptake. For confirmation ion-exchange mechanism in sorption process of Co(2+) ions by DAS scanning electron microscopy and EDX analysis were used.