Biosorption process for treatment of electroplating wastewater containing Cr(VI): Laboratory-scale feasibility test

Brown seaweed Ecklonia biomass was used for the treatment of electroplating wastewater that contains chromium and zinc ions. Batch experiments showed that Cr(VI) was removed from the wastewater through reduction to Cr(III) by contact with the biomass, whereas Cr(III) and Zn(II) were removed through adsorption to the binding sites of the biomass. Among various parameters, the solution pH most significantly affected the biosorptive capacity of the biomass. As the solution pH increased, the removal efficiency of Cr(VI) decreased, whereas that of Cr(III) and Zn(II) increased, for pH <5. This divergence of efficiency, because of the removal mechanisms of chromium and zinc ions, necessitated a two-stage biosorption process for the complete removal of both ions from the wastewater. The first stage comprises the removal of Cr(VI) by reduction into Cr(III) and of total chromium by partial adsorption at a low pH (1.5-2.5), and the second stage the removal of residual total chromium and Zn(II) by adsorption at elevated pH (4-5). A series of two columns that contain the Ecklonia biomass with a pH adjustment step between column operations was successfully used as a feasibility test of the proposed process. In conclusion, the abundant and inexpensive Ecklonia biomass can be used in the two-stage biosorption process for the treatment of electroplating wastewater that contains Cr(VI) and other metal ions, because it shows the promise of being environmentally friendlier than any existing chemical treatment process.