Removal efficiency of Cu2+, Cd2+ and Pb2+ by waste brewery biomass: pH and cation association effects

In this work two distinct (flocculent and non-flocculent) yeast wastes from Portuguese breweries were used for the selective removal of Cu2+, Cd2+ and Pb2+ from aqueous solutions. One of the goals was to establish both the pH profiles for the removal of each metal ion (1.0 mM) and the effect on the biomass biosorption capacity of pH adjustment during the process. The effect of the presence of multiple metal ions, in the 0.1–1.0 mM range, on metal removal efficiency was also studied. The results showed that, in the absence of pH adjustment, the optimum initial pH for the removal of three cations was in the 4.5–5.5 range for both types of biomass. However, a gradual pH increase was observed during the removal process, up to a final equilibrium value of 7.0–8.0. Regarding the biomass efficiency for metal removal in multi-cation systems, it was verified that only Cu2+ was significantly affected by the presence of the other metals in solution and only when the non-flocculent yeast biomass was used as biosorbent. Cd2+ was only slightly affected by the presence of both Cu2+ and Pb2+, and Pb2+ removal was not affected by the presence of any or both of the interferent metals for the two biosorbents used in this work. The highest and lowest metal removal yields were obtained for Pb2+ and Cu2+, respectively.

Waste brewery biomasses of non-flocculent and flocculent types were found to be promising biosorbents for the removal of Cu2+, Cd2+ and Pb2+ in concentrations up to 1.0mM from unbuffered aqueous solutions. The experimental conditions which led to higher metal removal yields were initial pH in the 4.5– 5.5 range and no adjustment or control of the pH during the biosorption process. Metal removal, however, was shown to be strongly affected by changes in the solution pH, further investigation into this effect being required. On the whole, removal capacities for one metal, with both waste biomass types, did not suffer significant interference from the presence of one or two of the other metals, which favours the use of this biosorption system with multiple-solute effluents. The copper removal capacity of the non-flocculent strain was, however, negatively affected by the presence of the other metals, an effect that was much less significant with the flocculent biomass. The inverse, though only for the more concentrated three-metal systems, was observed for Cd2+. These results suggest that different metal binding sites are available in the two waste biomass types, possibly also related to their flocculent /non-flocculent character. Although Unicer cells showed to be more efficient to removed Cu2+ than the Centralcer ones, in general, the higher metal removal yields were obtained using the biomass from Centralcer as biosorbent.