Biosorption of chromium, copper and zinc by wine-processing waste sludge: single and multi-component system study

Wine-processing waste sludge (WPWS) has been shown to have powerful potential for sorption of some heavy metals (i.e., chromium, lead and nickel) in single-component aqueous solutions. But although most industrial wastewater contains two or more toxic metals, there are few sorption studies on multicomponent metals by WPWS. This study has two goals: (i) conduct competitive adsorption using Cr, Cu and Zn as sorbates and examine their interaction in binary or ternary systems; and (ii) determine the effects of temperature on the kinetic sorption reaction. The sludge tested contained a high amount of organic matter (38%) and had a high cation exchange capacity (CEC, 255 cmol(c)kg(-1)). Infrared analysis reveals that carboxyl is the main functional group in this WPWS. The (13)C NMR determination indicates alkyl-C and carboxyl-C are major organic functional groups. At steady state, there are about 40.4% (Cr), 35.0% (Cu) and 21.9% (Zn) sorbed in the initial 6.12 mM of single-component solutions. Only pseudo-second-order sorption kinetic model successfully describes the kinetics of sorption for all experimental metals. The rate constants, k(2), of Cr, Cu and Zn in single-component solutions are 0.016, 0.030 and 0.154 g mg(-1)min(-1), respectively. The sorption of metals by WPWS in this competitive system shows the trend: Cr>Cu>Zn. Ions of charge, hydrated radius and electronic configuration are main factors affecting sorption capacity. The least sorption for Zn in this competitive system can be attributed to its full orbital and largest hydrated radius. Though the effect of temperature on Zn sorption is insignificant, high temperature favors the other metallic sorptions, in particular for Cr. However, the Cr sorption is lower than Cu at 10 degrees C. The Cr sorption by WPWS can be higher than that of Cu at 30 degrees and 50 degrees C.