Treatment of acid mine drainage: I. Equilibrium biosorption of zinc and copper on non-viable activated sludge

Biosorption is potentially attractive technology for treatment of acid mine drainage for separation/recovery of metal ions and mitigation of their tox icity to sulfate reducing bacteria. This study describes the equilibrium bi osorption of Zn(II) and Cu(II) by nonviable activated sludge in a packed co lumn adsorber. The Zn(II) uptake capacity of unconditioned sludge (not subj ected to processing other than drying) was found to decrease in repeated ad sorption-desorption cycles, declining by a factor greater than 20 from cycl e 1 to cycle 6, Equilibrium uptake of metals by dried sludge conditioned by exposure to deionized water at a pH corresponding to that of the feed solu tion showed a strong pH dependence and was modeled using the Langmuir adsor ption isotherm. Equilibrium metal uptakes from solutions containing single metal ion were 2.5 mg g(dry biomass)(-1) and 3.4 mg g(dry biomass)(-1) for Zn(II), and 1.9 mg g(dry biomass)(-1) and 5.9 mg g(dry biomass)(-1) for Cu( II) at pH 3.0 and 3.8, respectively. Equilibrium uptakes from binary mixtur es were 30% lower than single component solution uptakes for both metals, i ndicating some competition between the two metals. No hysteresis was detect ed between adsorption and desorption equilibria. Anion concentration and pH measurements indicated that simultaneous sorption of metal cation and sulf ate anion was probably occurring at pH 3.0, while proton exchange predomina ted at pH 3.8. Results of the study point to the usefulness of non-viable a ctivated sludge as a biosorbent for recovery/separation of metal ions from acid mine drainages. Published by Elsevier Science Ltd.