Toxic and radiotoxic metals of liquid wastes are sorbed by the sludge of Waste Water Treatment Plants (WWTPs) with a high efficiency.. Sludges with low toxic metals concentrations can be temporally stored or utilized as soil conditioners in agriculture. Other possible and economically acceptable way is repeated utilization of the sludge as heavy metals sorbent. Since effluents can contain several metals, it is necessary to study the simultaneous sorption of two or more metal ions and also to quantify the mutual effect of one metal on the other. In the present study, we have undertaken the study on the sorption characteristics of Dried Activated Sludge (DAS) from industrial WWTP for sorption Co2+ and Zn2+ ions from their binary aqueous system in batch experiments using radiotracers 60Co and 65Zn technique. Values of maximum sorption capacity (Qmax) of DAS at pH 6 calculated from extended Langmuir adsorption isotherm were 247 ± 15 μmol g-1 for Co2+ and 479±32 μmol g-1 for Zn2+ ions. Results revealed that the sorption capacity of DAS for both the metals increases with increased initial concentration in the range 100 – 4000 μmol dm-3 CoCl2 and ZnCl2, respectively. Presence of Zn2+ ions as co-ions caused more significant decrease of Co2+ uptake in binary Co-Zn system than vice versa. Experimental data Co and Zn sorption in binary system were well described by extended Langmuir model and affinity parameter b indicate higher affinity of DAS to Zn2+ in comparison with Co2+ ions. Prediction of total Co-Zn sorption by DAS using extended Langmuir model was less suitable due to dissimilarity of Qmax value of DAS for Co2+ and Zn2+ in single systems.
Key words: sorption, activated sludge, Co-Zn system, 60Co, 65Zn
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